When calculating the charging time of batteries, there are sometimes many factors that must be taken into account.
Basically, the following formula applies:
Charging time in minutes = (nominal capacity in Ah divided by charging current in A) * efficiency of the charger
The efficiency of the charger is a quotient of the charger's loss rate. Because with most chargers, around 20% to 25% of the power is lost. Very good (and expensive) chargers usually only have a performance loss of around 10%.
The charging process of the charger can also have a major impact on the charging time. There are different charging methods such as B. the «pulse charging process», «constant voltage charging process» or «constant current charging process».
The constant current and constant voltage charging methods are used for lead, lithium-ion and lithium-polymer batteries.
Battery type, number of cells, charge rate, charger performance?
The battery type determines how exactly the charging time is calculated. NiMH and NiCd rechargeable batteries, for example, can be identified by the printed designation «AA», «AAA», «AAAA» or «C». Lithium-polymer (Li-Po), lithium-iron phosphate (LiFePO4) and lithium-ion (Li-Ion) batteries usually have this designation or the short form printed on them.
The number of cells and the charging rate are also printed on batteries where this is required to calculate the charging time. The number of cells is given as xS, where x stands for the actual number of cells, so a battery with 2 cells would have “2S” printed on it. The charging rate is given in C, C is a factor that indicates the maximum discharge/charge current of the battery in relation to its capacity.
Attention: There is a C value for that unloaded and a C value for that Shop of the battery. The C value for charging the battery is significantly lower than the C value for discharging!
The less «C» used in practice, the longer the battery life. It should also be noted that the C rates given 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.