Battery Terminology – Glossary of Terms and Definitions

This list of battery terms lists the most commonly used terms and some uncommon terms that newbies in battery world will need defined.

The list is made with most readers in mind. Therefore highly technical terms are omitted.

Pretty much everything is covered that is needed to have a deep understanding of battery technology with some overly technical terms being left out.

Well let’s see that list now!

Table of Contents show

Battery Terms List



Accumulator is an energy storage device. In the battery sense it is a rechargeable (secondary) battery/cell.

Alternative Current AC

An alternating current is a current which flows in both directions as it is alternating between positive and negative many times in a second. This is the type of current present in your household outlets.

Amp or Ampere (A)

Named after the French physicist Andre Marie Ampere. Amp is a unit of measurement that measures electrical current. One Ampere represents the amount of current that is produced by an electromotive force of one volt pushing through the resistance of one Ohm. Amp abbreviation is letter A.

Amp Hour or Ampere-Hour (Ah)

Ah is a unit of measurement of battery’s capacity. Electrical storage capacity to be precise. This one is tricky because it actually represents how much capacity the battery has but presented in time measurement. Current multiplied with time in hours gives you the ampere-hours. This presents the amount of current the battery can hold and discharge in one hour on a single discharge. For example, a battery that is marked 10Ah can output 10A in one hour. If you discharge it with a 5A load then it will last for two hours. And if you discharge it at 20A it will last half of an hour. 1Ah is equal to 1000mAh.

Actual or Available battery capacity

This measurement may be different than the rated battery capacity because it represents the available capacity to perform work. It is expressed in Ah or mAh. The actual battery capacity depends on a lot of factors like discharge rate, charging method, temperature, ambient conditions, age of the battery and cut off voltage.


The negative electrode during the discharge of the cell is called anode. However, during the charge, it is reversed and the positive electrode is the anode. The anode releases electrons during the discharge to the circuit.

Aqueous Batteries

The batteries that use water-based electrolytes.

Acid Battery

These batteries use acid for electrolytes. A good example is a well-known Lead-acid battery which uses a sulfuric acid.

Active Material

These are chemically active parts of the battery/cell that convert from one composition to another which produces electrical energy (electrical current).


Alkaline batteries are well known in household battery types like AA cells. They are non-rechargeable or primary cells and are often used in various electronic devices like TV remotes, CD players, radios and etc. Alkaline cells deliver up to two twice the amount of energy the Zinc/Carbon cells do. The alkaline is not an environmentally friendly option because they are not rechargeable.

Ambient Humidity

The humidity in the surrounding of the operating battery.

Ambient Temperature

The temperature of the surrounding of the operating battery.

Absolute state-of-charge or ASoC

The new battery’s ability to take the defined amount of charge.

Absolute state-of-health or ASoH

The new cell/battery ability to store energy.



While this common term is often used for single cells like AA, AAA, 9V or similar “batteries” this term is actually used to define two or more cells that are connected electrically in series or in parallel. The battery is an electrochemical device composed of multiple cells and it is used to store energy.

Battery Capacity

It is most often expressed in watt-hours and ampere-hours or milliampere-hours. The watt-hours is a preferred battery capacity unit of measurement among engineers and more keen battery enthusiasts but many commercially available cells/batteries use the Ah unit. Wh (watt-hours) is equal to the capacity in Ah multiplied by the voltage of the cell/battery and is a more accurate measurement of capacity.

Battery Charger

This is a device that is used to recharge the rechargeable (secondary) battery.

Battery Charge Rate

It is expressed in A or mAh and represents a current rate at which the battery is charged. It is usually specified by the battery manufacturer. The battery charge rate must not exceed the upper limit specified by the manufacturer.

Button Cell

A cell that has its height dimension smaller than its diameter. They look like a shirt button. Button cells have a distinct electrode shape that is in a form of a disc. It is also known as a coin cell and they are usually non rechargeable.


Battery energy storage system (also referred to as ESS).

BMS or Battery Management System

This system can be used internally or externally with a battery to manage charge and discharge, add certain protections, provide a state of charge and others. It is one of the most important elements in keeping a battery safe and long living.


Cutoff Voltage

The cutoff voltage of the battery/cell is the lower-limit voltage at which the battery discharge is total. There is a difference between battery cutoff voltage and the required voltage by the device. If the device has a higher cutoff voltage than the battery, the battery will still have some useful capacity left which the device can’t use. The cutoff voltage for batteries depends on the chemistry mostly. NiMH and NiCd batteries will usually have a cutoff voltage of about 1V, the Li-ion batteries reach cutoff voltage at 3.0V, LiFePO4 at 2.5V and so on.


C is a measurement that is used to specify a charge or discharge rate equal to the capacity of the battery. A battery that has 2000mAh of capacity or 2Ah would have a C of 2A. 1C=2A. If you needed to charge that battery with half of the C or C/2 you would charge it with 1A because 2A/2 equals 1A. If you had to charge it with C/5 it would be 0.4A or 400mAh. The same goes for discharge. 5C discharge would be 5*2A in that example which is a discharge of 10A.


See battery capacity above.

Capacity Offset

A correction calculation of the battery rated capacity if discharged with a different C rate than for which it is rated for.


A primary battery that is commonly used in small household devices like calculators, alarm clocks, TV remotes and similar. It is still commonly used thanks to its low price.


Cathode absorbs the electrons. During the discharge, this electrode is the positive electrode in a voltaic cell. Same as with the anode, during the discharge, it reverses and becomes the negative electrode.

Cadmium Cd

A toxic metal often talked about in the battery world because it used to be often used in battery chemistries. Specifically Nickel-metal cadmium batteries or NiCd. Batteries containing Cadmium are shunned today and most of them are banned for use unless in situations where it is justified.


The cell is a single building block of a battery that is composed of multiple cells. The cell is an electrochemical device that contains positive and negative plates and electrolyte. The purpose of a cell is to store electrical energy or charge.

Cell Mismatch

Cells that have different capacity and voltage levels within a battery pack.

Cell Reversal

A phenomenon when the stronger cells within a battery pack force a voltage of reverse polarity to a weaker cell during a deep discharge. This can be fatal for batteries of some chemistries. If you must do a deep discharge on a cell basis it is best to disassemble the battery pack and do them separately to avoid cell reversal.


Charge is a conversion of electric energy into chemical energy inside a battery or cell. The charge is received in the form of a current.

Charge Rate

Charge rate represents the amount of current that is applied during the charging of the battery. It can vary during the charge. The charge rate is presented in C or a fraction of the C. For example, a charge rate of C/2 with a battery of 2000mAh capacity would be 1A of charge current.


Process of providing electric energy to the battery in order to store it as chemical energy. The charging process reverses the process in rechargeable batteries after they have been exhausted so that they are charged again.

Change in Temperature (ΔT)

Feature of chargers that terminate the charge when they detect the difference between ambient temperature and that of the cell.

Change in Temperature/Change in Time (dT/dt)

Feature of chargers that terminate charge upon detecting the change in temperature over time. A much more favorable detection method because it detects rapid temperature buildup just before the cell reaches the full charge. This is not used with all battery chemistries.

Charge Acceptance

The amount of current a battery can accept at a specified temperature and charge voltage in the defined period.

Charge Efficiency

Represents the ratio of a cell’s output during discharge to its input during charge.

Charge Retention

Capacity that remains in the battery after being stored for prolonged period of time.


Conditioning the battery usually means discharging it completely before charging it completely in order to restore its maximum capacity. It can help with the perceived memory effect of NiCd batteries but it can be applied to other chemistries as well.

Constant Current Charge

This process occurs either as a part of the charging process or as the entire charging process. The constant current charge has a constant amount of current applied to the battery as the name suggests.

Constant Voltage Charge

The constant voltage charge is a process in which the charging voltage doesn’t change while the charging current can vary. It is usually a part of the saturating process of charging the battery that comes after the constant current charge process.

Continuous discharge rate

The CDR is a rating designated by the manufacturer. The battery can be continuously drained with the specified continuous discharge rate safely or under this value. The CDR is usually given in Amps.


Unit for electric charge. A single coulomb 1C is equal to one ampere-second 1As.

Coulombic efficiency / faradaic efficiency

A charge efficiency of electrons that are transferred to battery.


A single process of charge and discharge of the battery.

Cycle Life

Cycle life presents a total number of charge and discharge cycles the battery/cell can endure before its capacity is significantly reduced. Different battery chemistries have different values for cycle life. End of battery life is usually rated for when the battery has left 80% of its rated capacity.

Cylindrical Cell

A cell in a cylindrical form as opposed to a prismatic cell.


Deep cycle

A cycle that discharges the battery until it reaches its cut-off voltage.

Deep-Cycle Battery

Deep cycle battery is designed to be continuously deeply discharged.

Direct Current DC

Electrical current type. In the sense of batteries this means that one terminal is positive and another negative.

Delta V

Detection mechanism of some battery chargers which detects the voltage drop occurring when the battery reaches its maximum capacity.


Spending the stored energy in the battery using a power-demanding device. In a chemical sense, this means converting the chemical energy of the battery into electric energy.

Deep Discharge

Using all of the available electrical energy in the battery until it reaches the cutoff voltage.

Discharge, high rate

Fast energy withdrawal from the battery. Using a high rate of current load to discharge the battery.

Discharge, low rate

Using the energy in the battery to power a device with a low rate of current load. Discharging the battery this way takes a long time because its stored energy is used slowly.

Discharge Voltage

The voltage on the battery terminals while it is being discharged.

Depth of Discharge DoD

The depth of discharge represents how much of the battery capacity has been removed from it. It is most often presented as the percentage of the battery capacity. If you wanted to say that the battery has spent half of its capacity you would say that it is at 50% depth of discharge. In another example, a 70% depth of discharge would mean that 70% of the energy has been spent with 30% capacity remaining for use.


Withdrawing the current from the battery/cell.

Dry Cell

Dry cell is a primary cell in which the porous medium absorbs the electrolyte.

Dumb Battery

Battery pack which doesn’t have internal circuitry that enables communication with the user.

Driving range

Electric vehicles will rather display possible driving range than battery capacity.


Electrochemical Couple

A system of chemical materials in the cell that represents electrical energy storage through the electrochemical reaction.


The electrolyte in batteries is a chemical compound that conducts the electric current when it is fused or dissolved with specific solvents. The water is a usually used solvent. When electrolytes are in the fused state or in solution, the rise in ions follows, which conducts the electrical current.


In a broad sense, an electrode is an electric conductor which serves as a pathway for electric current to enter or leave a conducting medium. The conducting medium can be solid, solution, electrolytic solution, molten mass, vacuum or gas. In the battery sense, the electrode is the same thing but more specifically defined it is a conductor or a plate in the cell where the electrochemical reactions occur.


Electropositivity is the degree to which an entity in the galvanic cell will operate as the positive element of the cell.

Electronic Tester

A device which detects the condition of the cell/battery by ohmic measurement like internal resistance or conductance.

End-of-Discharge Voltage

The cutoff voltage. This is the voltage when the cell terminates a discharge.

Energy – Output Capability

The energy that is stored in the cell or a battery pack that is expressed in watt-hours.

Energy Density

Weight or volume to cell energy ratio. It is expressed in watt-hours per kilogram / pound or watt-hours per cubic inch / centimeter.


Final Voltage

Same as cutoff voltage.

Float Charging

Float charging is the charging step that is applied to top off the secondary battery and keep it in fully charged condition. The float charging constantly applies the constant voltage energy supply and is typically used with the lead-acid batteries but can be applied to other chemistries as well.

Fast Charge

Fast charging the battery is hard to precisely define but typically it means charging the battery faster than usual. This depends on the chemistry, capacity and other factors. When we say that the battery can be fast-charged that means that for that particular chemistry the battery is designed to be an exception and it can take a faster charge than usual for that chemistry. Alternatively, we can talk about it in hours and say that all batteries within a certain chemistry are fast charge capable because relatively speaking they do charge fast because they charge in 1-3h intervals.


Galvanic Cell

Combination of electrodes that are separated from each other by an electrolyte. This combination is able to produce electrical energy by electrochemical reaction.


Gassing refers to the evolution of gas from a single or both electrodes in the cell. Gassing in the cell is the result of self-discharge or from the electrolysis of water in the electrolyte while charging.

Gravimetric Energy Density

Gravimetric energy density is the ratio of battery energy to its weight. It is also referred to as power density and is most commonly presented in Watt-hours per kilogram Wh/kg.


Graphite is a form of carbon that has hexagonally crystallized allotrope. It is used as anode in most Lithium ion batteries.


High rate discharge

Discharging the cell at a high rate in comparison to its capacity.

Hysteresis charge

Charger stops charging when battery is at full capacity but it continues charging after a certain period of time to compensate for self-discharge and various parasitic loads.


Halon is used to suppress Lithium-ion battery fire.

Hertz (Hz)

Hertz is a unit of frequency. 1Hz constitutes one full cycle per second.


Internal Resistance

The internal resistance of a battery represents the resistance to the flow of the electric current inside the cell(s). The unit of measurement is milliohms. The quality battery will have low internal resistance but this will change during the lifespan of the cell(s).

Impedance Intermittent Test

This test is used for the battery’s internal resistance. For the duration of the test, the battery is subjected to different periods of discharge and rest according to the specific discharge regimen.

Intelligent battery

Unlike the dumb battery described above, the intelligent battery contains internal circuitry that enables it to communicate with the user. This means that the battery can indicate its capacity and similar information or have a special external bus to interface with intelligent chargers and the devices the battery is powering.

Internal Pressure

A pressure that occurs within a sealed battery that is a result of hydrogen or oxygen evolution within the battery.

IR Drop

A voltage drop that results from the internal electrical resistance or electrical current flow in the cell. This voltage drop is a product of the current (amperes) and the internal resistance (ohms).

Intrinsically safe battery

These batteries have special protection circuit that is built-in. They enable safe functioning of the battery even in hazardous area.


Ion is an atom or a molecule that has unequal number of protons and electrons. They provide positive or negative electrical charge.


Joule (J)

Joule is an energy measurement unit. A single joule represents one ampere at one volt for one second and it is also applied to mechanical energy. The formula is as follows: 1J= 1A at 1V for 1s.


Lead acid battery

One of the most popular batteries. Lead-acid battery is mostly used in the automotive industry but it has a vast scope of use in general. This is a low-cost battery that has a decent life duration and offers a good voltage per cell. Some of the biggest issues the lead acid battery has are the poor temperature characteristics, weight and the fact that it can’t be in the discharged state for prolonged periods without getting damaged. Lead acid battery is made up of plates, lead and lead oxide with various other additive elements to influence battery characteristics. It works with a 35 percent sulfuric acid and 65 percent water solution as the electrolyte.

Lithium (Li)

Lithium is a soft silver-white metal that belongs to the alkali metal group. Lithium is highly used in battery technology today and its use will only increase in the future. Lithium represents the element of the future.

Lithium battery

Lithium battery is in almost every case non-rechargeable. They have a lithium metal anode and shouldn’t be confused with rechargeable lithium-ion cells. Lithium batteries are replacing alkaline single use cells and especially household batteries like 9V battery, AA cells and similar. They are a more expensive single use choice but are way more energy dense.

Lithium Ion

Lithium ion batteries are quite diverse. A lot of different chemistries fall under the category of lithium-ion batteries. But usually, when we talk about lithium ion cells we are talking about cells that have a graphite anode and a lithium manganese oxide or lithium cobalt oxide cathode with/or a combination between these elements and additives like nickel and silicon. Li-ion batteries are advanced technology that is used for rechargeable secondary batteries. They offer much better characteristics than NiMH and NiCd cells which is a reason they are replacing them in many use cases.

Lithium-ion batteries are most used for electric vehicles, electronics like phones, tablets and laptops.

Lithium Iron Phosphate LiFePO4

Lithium iron phosphate is a type of a lithium ion battery that has distinct characteristics. They are mainly characterized by the substantial increase in safety and cycle life. Additionally, they offer a very high discharge rate. Other lithium-ion chemistries can’t compete with LiFePO4 when it comes to these characteristics. However, they suffer from lower energy density and voltage.

Lithium Polymer Li-Po

Another li-ion type. The Li-Po is characterized by its distinct shape and construction abilities. It can be made in a thin pouch form as they allow for very flexible packaging, low cost and are a bit safer than most other li-ion chemistries. Li-Po is also known as a solid state battery. It uses solid polymer as electrolyte.

Load Current

The current that is drawn from the battery.

Load Tester

A device that draws the current from the battery while measuring the voltage. This determines the ability of the battery in a real use case scenario and is a way more accurate depiction of the battery condition.


Manganese (Mn)

Often used as a cathode material in li-ion cells.

Memory Effect

Memory effect is a phenomenon mostly attributed to NiCd and NiMH cells that temporarily lose their maximum capacity when operating in successive cycles with less than the full depth of discharge. The battery memory effect can be reversed by performing a full discharge and charge.  It should be noted that the true memory effect is something entirely different and it only happens with sintered plate nickel cadmium batteries. The true memory effect is permanent.

Midpoint Voltage

The battery’s voltage on the middle of its discharge cycle.


Milliamps is a measurement of battery capacity and represents one thousand of an Amp. 1mA=1A/1000 or 1mAh=1Ah/1000.


Negative Terminal

The terminal from which the electrons flow in the external electric circuit when the cell is discharging.

Negative Electrode

The negative electrode in the cell is the anode during the discharge.

Nonaqueous Batteries

Batteries whose cells don’t have water in them. Organic electrolytes or molten salts can be used as the examples.

Negative Delta V (-ΔV)

Some quality chargers utilize the negative delta V to terminate the charge. Negative delta V is a drop in voltage that happens when a battery is fully charged.

Nickel Cadmium NiCd

Nickel Cadmium or NiCd for short is one of the most proven batteries in history. It was widely used thanks to its high discharge rate, excellent reliability, robustness, and performance in tough temperature conditions. Today it is not used very often because it contains a toxic chemical Cadmium that is really bad for the environment. Additionally, this chemistry has a low capacity when compared with most modern chemistries and especially lithium ions. Today the NiCd is still used when necessary and sometimes still in power tools.

Nickel Metal Hydride NiMH

Nickel metal hydride batteries or NiMH for short are a much better choice than NiCd because they are not toxic and have higher capacity. They are widely used for rechargeable household batteries like AA, AAA and other cells, wireless phones, camcorders, radios and other devices.

Nominal capacity

The nominal capacity of the battery represents the capacity the manufacturer has stated. This capacity depends on the testing conditions and may not be the actual capacity you get from the battery.

Nominal Voltage

The nominal voltage of the battery is a voltage rated by the manufacturer.


Ohm’s Law

Ohm’s law states that in a given electrical circuit, the amount of current in amperes (I) is equal to the pressure in volts (V) divided by the resistance, in ohms (R). Ohm’s law is basically the formula that is used to describe the amount of current flowing throughout the circuit.

The Ohm’s law can be applied in these three formulas that are important for battery related fields:

  • I = V/R – This formula is used to calculate the amount of current in amperes I.
  • V = I x R – This formula is used to calculate the voltage pressure V.
  • R = V/I – This formula is used to find the resistance in ohms or R.


A measure of resistance that causes one volt to produce a one ampere current.

Open Circuit

Open circuit in the battery sense is a condition in which a battery is not charging or discharging because it is disconnected from a circuit. Basically a battery with open terminals that are not a part of a circuit.

Open-Circuit Voltage OCV

When the circuit is open there is a difference in potential between the terminals of a cell/battery and we call this the open circuit voltage.


Oxidation battery term is used to describe a chemical reaction by the electrode’s active material that is producing a release of electrons.

Operating voltage

Operating voltage is the voltage between the two battery terminals when it is without any load.


Overcharge is a battery term often used to describe the battery condition when it is forced to receive additional current after all the active material has been converted to the charged state. Overcharging the battery basically continues charging it after it has reached a 100% of its charge capacity. In almost every case this is detrimental to the health of the cell. Some chemistries can tolerate a little bit of overcharge while others are very sensitive to it. Overcharging the battery can lead to build up of heat, gas production and venting of the cell. In unstable chemistries, it can lead to a fire.


Over discharging the battery means discharging it beyond its cut-off voltage. This is almost always detrimental to cell health and can even lead to voltage reversal.


Parallel Connection

Parallel battery connection is the arrangement of cells within a battery pack made by connecting every positive terminal together and every negative terminal together. The voltage of such a battery is equal to the voltage of the individual cell. The capacity of this battery gets increased in proportion to the number of cells in the pack.

Parasitic load

Parasitic load on a battery is the power consumption that occurs when the device is turned off. Not all devices are optimized to reduce the parasitic load so if you don’t plan to use a battery powered device for a longer period of time, it is wise to remove the batteries.


Polarity is a battery term used to refer to the charges existing at the battery terminals.

Polarity reversal

Polarity reversal of cell terminals happens because of over discharge and it can happen to a single cell in a battery pack.

Peukert law

Peukert’s law is used to calculate the battery capacity for varying discharge rates. Usually, discharging the battery with a higher discharge rate will decrease its capacity and using Peukert’s law we can approximate the actual capacity under the specific discharge rate. This law is mainly used for lead acid batteries.

Positive Terminal

The positive terminal of a battery receives the electrons flow from the negative battery terminal after they flow through the external circuit (i.e. a battery powered device) during the battery discharge.

Positive Electrode

Electrode of a battery or cell acting as the cathode during discharge.

Primary Cell

The primary cell is a non-rechargeable cell. That is because its electrochemical reaction that produces the electric current is not efficiently reversible. Once a primary cell is discharged it cannot be recharged by the electric current. These disposable batteries are not an ecological solution and should be replaced with rechargeable (secondary) cells whenever possible. However, there are reasons why it is justified to use primary cells. These cells are mostly available as lithium, alkaline or zinc-based household primary cells.

Primary Battery

Primary battery is made using one or more primary cells. Therefore it is non rechargeable.

Peak Voltage Detection (PVD)

Peak voltage detection is a detection mechanism some battery charges utilize in order to determine when the battery has reached its maximum capacity. Once the charger detects the voltage of the cell matches with its peak voltage it stops supplying the charging current.

Permanent charge

Continually maintained charging current regardless of the battery state of charge.


Potential in the battery terminology represents the energy of an electric charge that is quantified in its power to perform work. It is an electromotive force. The potential per unit of charge is the voltage.


Power represents the time rate of energy transfer and it is expressed in Watts (W). One watt is the rate at which electrical work is performed when one ampere (A) current goes through the electrical potential difference of one volt (V). The formula is 1W = 1V x 1A.

Prismatic Cell

In prismatic cells the positive and negative plates are stacked instead of being rolled like in cylindrical cells.

Pulse Current

Pulse current in battery terms means the occasional current discharge that is higher than what the battery is being drained at continuously.

Pulse discharge

Pulse discharge is a high drain discharge that happens in a short time interval. Usually in less than one second.


Salt or phosphoric acid.


Polymer in terms of batteries is an electrical insulator that passes ions.

Pouch cell

Pouch cells are packaged in flexible foil pouch packages that are heat-sealable. This battery design offers the most efficient use of space and has up to 95 percent of package efficiency. Exposing pouch cells to high humidity and heat will shorten their lifespan. Most often used for electronics like smartphones, laptops and similar.

Power Cell

Power cells are designed to output the maximum amount of current. These cells are often compromising other battery characteristics like energy density, stability, longevity and life cycle.

Power density

Power density in batteries refers to their volumetric power density. The amount of power that is stored in the volume of the cell / battery.

Protection circuit

Protection circuit in battery pack ensures safety when the battery is pushed over its design limitations.


Quick charge

Quick charge means charging the battery fast. Faster than its normal charge time rating. It can be achieved using a quick charger that is designed to work with the battery.

Quantity of charge

The amount of electric energy that is provided to the battery with the charger. It is expressed in Ah.


Rated Capacity

A specified number of ampere-hours or watt-hours by the battery manufacturer that the battery can deliver under specific conditions. The manufacturer rates the battery capacity under specific loads and conditions and this is called the manufacturer’s capacity rating.


Rechargeable battery is a secondary battery that can be recharged many times until it reaches its end of life.


Recombination happens in the battery when the gasses that are normally occurring within the battery are recombined into water.


Reduction is a chemical process in the battery that accepts electrons by the electrode’s active material.

Rapid Charge

Rapid charge is a rate of charge that recharges the cell or a battery to its maximum capacity fast. Usually in about 2 hours.


Reconditioning the battery is a process when one or more deep discharge cycles are performed with a low steady current. In batteries prone to memory effects, reconditioning helps in restoring the original battery capacity.


Recycling batteries is a process when the battery materials are fully or partially reclaimed without harm to the environment and human health. For some battery chemistries recycling is required by law while for others it is done for material reasons among others.

Resealable Safety Vent

This safety vent is built into prismatic and cylindrical cells and its purpose is to prevent the build up of big internal pressure.

Residual capacity

Residual capacity is the amount of charge left in the cell after it was used and prior to the next charge.


Resistance is the degree to which the flow of electrons is opposed by the electron passing materials. This resistance is measured in Ohms.

Relative state of charge RSoC

Relative state of charge or RSoC is the available battery capacity with the capacity fade.

Relative state of health RSoH

Relative state of health in batteries represents the available storage capability when the battery gets broken in through use.


Runtime is the length of time the battery can provide electric charge during its discharge cycle.


Safety Vent

Safety vent in batteries works as a safety mechanism that gets activated upon internal gas pressure rise that exceeds normal levels. We recognize two safety vent types in batteries the automatically resealable and unresealable.

Secondary Battery

Secondary battery is the battery composed of secondary cells and it is rechargeable.


Seal in batteries is the structural element of galvanic cells that prevents the solvent or electrolytes from leaving the cell while limiting the ingress of air into the cell. The purpose of preventing the air intake is to stop it from drying out the electrolytes or interfering with the chemical reactions occurring within the cell.

Sealed Cells

Sealed cells are closed and don’t release liquid or gas if used under the manufacturer’s specification. Since they are sealed they can’t receive electrolyte addition.


A separator in cells is a penetrable membrane that allows ions to pass through it but restricts electrical contact between the cathode and anode from happening.

Self Discharge

Self discharge is something that all batteries experience and it happens while the battery is in an open circuit or in other words when it is not in use. The battery simply continuously loses charge on its own. This is usually a slow process but it depends on the chemistry of the battery and the environment it is stored in.

Shelf Life

Shelf life in dry cells is the length of time at a storage temperature of 21 Celsius degrees (69F) after which the cell keeps a specific capacity percentage. It is usually rated by manufacturers to retain about 90% of its capacity. Long shelf life is especially important in primary batteries. If you are going to get a lot of disposable cells then they should last you long while in storage so that you can actually use them before they are dead on their own.

Series Connection

Connecting batteries in series is an arrangement of cells within the battery pack in which the cells are connected successively. The positive terminal of each cell is connected to the negative terminal of the following cell. Connecting batteries in series make their voltage cumulative while their capacity remains that of the individual cell in the pack.

Service Life

Battery service life is a period of useful life of the battery. This period is a time length before the battery reaches a predetermined end-point voltage.

SLA (Sealed Lead Acid)

Seal lead acid batteries are an inexpensive solution for secondary batteries used for energy storage.

Slow Charge

The slow charge for batteries is usually very good for their longevity. It is typically performed with low charging currents of about 0.1C of a battery and it may take an overnight charge to complete.

Smart Battery

The smart battery has internal circuitry that enables communication with the user. Some of them may feature a capacity indicator while others may offer an interface with the equipment the battery is powering.

Soft Cell

Soft cells experience a rise in voltage during charging that is beyond its defined boundaries. Such voltage rise can be explained by high cell impedance which could be a result of prolonged battery storage, lack of electrolyte in the cell and very cold cell temperature.

Specific Energy

Specific energy represents a ratio of the weight of the battery in relation to its energy output capability and it is defined as a gravimetric energy density Wh/kg.

Spiral Wound

Spiral wound is a special electrode structure that is characterized by a high surface area. It is created by winding the electrodes and separator into a spiral-wound jelly-roll like design.


Short circuiting the battery is usually a dangerous thing but in almost all cases it is really bad for the health of the battery. Short-circuiting happens when the electrical path between the battery terminals is accidentally created, otherwise known as the short path. Batteries can supply immense power outputs if short circuited and can melt the terminals, cause sparks and fires.

Short-Circuit Current

The current that the battery delivers when it is short circuited.

Shallow Cycling

Shallow cycling a battery means utilizing charge and discharge cycles where the battery is not being fully discharged by reaching its cutoff voltage. Some chemistries like NiCd really don’t tolerate shallow cycling as it can lead to memory effect while other chemistries like lead-acid should only be used that way.

Stationary Battery

A stationary battery is the opposite of mobile, that is, it is designed for use in a fixed location. These batteries are almost always secondary (rechargeable). They can be backup power, off-grid power source or even used to power whole parts of the city in case of a current outage.

Starting-Lighting-Ignition (SLI) Battery

SLI is a type of battery that is designed for starting internal combustion engines. It also powers all of the electrical elements in automobiles when the engine is not running and supplying the energy. SLI batteries are also used for emergency lighting as backup power sources.

Storage Battery

Storage battery is by definition a secondary rechargeable battery but unlike all other rechargeable batteries, the storage battery is economically justified because they are cheap enough to be used for large capacity storage. Synonyms for storage battery are accumulator, secondary battery and the secondary cell.

Storage Cell

Storage cell is a secondary cell that is economically feasible for use in large current capacities for storage.  They are rechargeable.

Stand-by use

Is the use of battery or cell in a way that keeps them constantly charged so that they are ready when the situation calls for power drain.

State-of-charge (SoC)

State of charge represents the charge level of the battery and it is usually measured and expressed in percent. It is not an indicative of the capacity.

State-of-function (SoF)

Shows battery readiness when it comes to capacity, current delivery, SoC, voltage, self discharge and a few other things. It is measured in percentages.

State-of-health (SoH)

Shows battery performance when it comes to capacity, current delivery, voltage, self discharge and a few other things. It is measured in % and it excludes SoC.


Silver-zinc is a rechargeable battery chemistry that has a high specific energy and is used for defense and aerospace. This is an expensive chemistry and it has a short cycle life.

Single-wire Bus

Simplified smart battery that has just one wire which provides the digital communication.


System management bus is a two-wire interface based on I2C. It forms a communication with the battery and the device by accepting control parameters. It provides battery status in terms of the state of charge, manufacturer information, error messages and cycle counts.


Spinel is a hard glassy mineral that is formed of magnesium oxide and aluminum. It is formed in a three-dimensional chemical structure. Manganese based lithium-ion cells have the spinel structure.


Spectroscopy is the analysis f the compound or a battery that is received when scanning with a frequency.


Taper Charge

Taper charging the battery basically means starting the charge with the high rate charging current while the battery is at a low state of charge and then as the state of charge increases, lowering the charge current rate. The charge current tapers off as the battery is nearing its 100% capacity.


Terminals are elements of the cell / battery that the external electric circuit connects so that the electric flow may commence from the battery.

Temperature Cutoff (TCO)

Temperature cutoff happens when a safety device within a cell / battery senses the high temperature in a cell and opens or cuts off the electrical circuit. This prevents any further increase in temperature of the cell that happens because of charge or discharge.

Thermal Runaway

Thermal runaway is a battery term used to describe a special condition where a cell that is being charged or discharged gets destroyed through internal heat generation. This heat is generated due to high overcharge or high rate of discharge or from other abusive effects.


Thermistor is a temperature sensing device. It is used to measure the temperature of a cell or a battery pack.


Thermostat in terms of batteries is a circuit protection device that is meant to prevent over temperature and over current states. The thermostat goes from a low-resistance state to the open circuit with a specific predetermined temperature.

Trickle Charging

Trickle charging the battery is a method that maintains the battery capacity and voltage charge. Not all battery chemistries tolerate well the trickle charging. A quality charger should be used to trickle charge.

Thionyl Chloride Lithium

Thionyl chloride lithium is a type of lithium battery that offers an incredibly long service life and low discharge rates. This chemistry can easily function well for 15-20 years. It is best suited for use cases where a low continuous current or moderate current pulses are expected and in locations where a physical approach is difficult. It has the highest energy density among the lithium battery family. This battery is manufactured in hermetically sealed cases that can be cylindrical, coin or wafer types. This is a non rechargeable battery.

Time Charge

Time charging a battery means using a charging method that terminates the charging process after a predetermined amount of time. It is usually a not reliable charging method that is used by less quality chargers. That is because this charging method will charge regardless of the battery’s state of charge and in turn can easily overcharge it.

Top-Off Charge

Part of a charging process that is meant to complete the charging process and get the battery to reach its 100% capacity. It is applied after the rapid charging that did not charge the battery to its maximum capacity. It is usually applied after the charger terminates the rapid charge because of a dT/dt termination.


Universal Serial Bus (USB)

A USB protocol that you normally find on electronic devices like laptops or PCs. In the battery terminology, you may see it too. It represents just that, a bi-directional data port featuring a 5-volt supply that can supply current to charge batteries.



A sealed mechanism that is meant to provide the controlled escape of evolving gases from within a cell due to an abnormal heat build up. Common in li-ion cells like 18650, 21700 and others. It is also used for some other chemistries. This is a very important safety feature.


Volt is a unit of measurement of electromotive force, or difference in potential, that causes a current of one ampere to go through the resistance of one ohm. The volt unit received its name after the Italian physicist Alessandro Volta (1745-1827).

Voltage Delay

Some batteries may develop a passivation film on the surface of the active material if they are left in open circuit storage. After this film is developed, the first discharge that follows may display a lower than rated voltage. This is solved by discharging and recharging the battery.

Voltage Depression

Voltage depression is a phenomenon in which the cell develops an abnormal voltage drop during the discharging.

Voltage limit

Voltage limits are often imposed on battery packs and even on individual cells that prohibit the battery to reach certain high and low voltages during the charge and the draining process.

Voltage Reversal

Voltage reversal in batteries happens when the battery is over discharged and it represents the change of normal battery polarity.


Voltmeter is a device with a purpose of measuring voltage and today it is usually digital.

Volumetric Energy Density

A ratio of the cell’s energy to its volume. It is most commonly expressed in Watt-hours per liter Wh/l. Also referred to as power density.

Valve-regulated lead acid (VRLA)

This is a lead acid battery that recombines oxygen (positive plate) with hydrogen (negative plate) on a charge. It is a maintenance-free. Valve regulates inside pressure by releasing any excess gasses but the repeated venting will dry it out eventually.

Vinylene carbonate

This is an additive that improves the performance of Lithium ion cathode.



Watt is a measurement of total power. The watt is obtained by multiplying amperes with volts.

Watt Hours (Wh)

Wh represents the amount of electric energy that is possible to withdraw from cell / battery under certain conditions.

Wet Cell

Wet cells are designed with electrolytes in liquid form which are free to move and flow.



Zinc-air is a primary battery that was often used for watches and hearing aid devices. They store a lot of energy per unit of weight. The zinc-air battery has very low current load abilities.


Zapping in battery terminology is used when describing the application of a momentary current pulse in order to evaporate a short.


This was a list of useful battery terms that will be interesting to most readers. Since the field of battery technology is very complex the terminology can be overwhelming so this list provides introductory and medium terms when it comes to complexity. Highly technical words were not listed here.

If you think that a specific term is missing or that something could be worded better please don’t hesitate to shoot an email on the contact page.

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