Calculate battery charging time - How to do it?

When calculating the charging time of batteries, there are sometimes many factors that must be taken into account. Basically, the formula is: Charging time in minutes = (nominal capacity in mAh divided by charging current in mA) * efficiency of the charger. The efficiency of the charger is a quotient of the loss rate of the charger, because most chargers lose about 20% to 25% of the power, very good (and expensive) chargers usually have a power loss of only about 10%.

The charging method of the charger can also have a major influence on the charging time. There are different charging methods such as the "pulse charging method", "constant voltage charging method" or "constant current charging method".
For lead-acid, lithium-ion and lithium-polymer batteries, the constant-current and constant-voltage charging methods are used. Our online calculator calculates the charging time based on the constant current charging method.

Battery type, cell count, charge rate, charger performance?

The battery type determines how exactly the charging time is calculated. NiMH and NiCd batteries, for example, can be recognized by the printed designation "AA", "AAA", "AAAA" or "C". Lithium-polymer (Li-Po), lithium-iron-phosphate (LiFePO4) and lithium-ion (Li-Ion) batteries normally also have this designation or the abbreviated form printed on them.

The number of cells and the charge rate are also printed on batteries where these are required for calculating the charge time. The number of cells is indicated with xS, where x stands for the actual number of cells, so a battery with 2 cells would have "2S" printed on it. The charge rate is given in C, C is a factor that indicates the maximum discharge/charge current of the battery in relation to its capacity.
Note: There is a C value for discharging and a C value for charging the battery. The C value for charging the battery is significantly lower than the C value for discharging!

The fewer "C "s used in practice, the longer the battery life. It should also be noted that the C rates indicated on the batteries are often too high (for advertising purposes). It is therefore better to use a little less "C" than printed on the battery.