# Battery Charge Time Calculator With Variable Efficiency Levels

It is somewhat complicated to estimate the charging time of your battery which is why I made this simple online battery charge time calculator.

This calculator estimates the battery charging time and allows you to modify the efficiency level of the charge cycle.

If charging batteries worked in ideal conditions it would be as simple as dividing the capacity of the cell and the charging current but there are hundreds of variables that can impact the battery charging efficiency. You can read more about it beneath the calculator.

## How to use the battery charge time calculator?

First input the capacity of your battery in mAh. Look for this information on your battery or the spec sheet. If it is given in Ah then multiply it by 1000 to get the mAh value.

Second input the charging current in mA. If your charger states the charging current in A, just multiply it with 1000. For example if the charger outputs 0.5A that would be 500mA. An output of 3A would be 3000mA.

That’s it. You will get the value in time and decimal format. If you want you can modify the charge efficiency to get more accurate reading instantly.

## What is your specific case charging efficiency?

Answering this question is very difficult. Unless you have various measuring equipment you are not going to figure this one out with high precision. But even if you did you would need to dedicate some time to figure this out.

This depends on the battery chemistry, quality of manufacturing, internal resistance (which may not be the same as when the battery was new due to wear of use), ambient temperature, charging current (can increase internal temperature of the cell), quality of charger and other things.

It is best to just stick with about 90% charge efficiency if your battery is of good quality and you are using a good charger. Using 80% in the calculation is also very accurate and especially if the battery is not in a near new condition.

Feel free to experiment with different charge efficiencies. Use this calculator in tandem with the real world scenario of your charge cycle. But if you must rely on the calculation only you can use the calculator or use my method explained below.

## How does the calculator work?

In short, the calculator takes the value of battery capacity and divides it with the charging current which is multiplied by the charging efficiency number that is multiplied with one percent value.

Here is the formula that gives the charge time in decimal hours:

Battery capacity x (Charging current x (Charging efficiency x 0.01)) = Initial result in decimal hours.

This value is then divided into two parts. A rounded number and “what is left” from the decimal point. The rounded number represents the hours and the number from the decimal point needs to be iterated through another equation in order to return the minutes value.

Here is the formula that returns the minutes value:

(Initial result in decimal hours x 60) – (The rounded number of the decimal hours x 60) = minutes.

The calculator was written in JavaScript so your browser should enable it. Almost every browser today does so you are covered.