Battery Life Calculator, Formula, Example, Formula

Battery Life Calculator:

Enter the battery capacity of the battery, input voltage and the total load; then press the calculate button to get the battery life in hours.


Enter Battery Capacity: Ah
Enter battery voltage: V
Load W
Result Battry Life: Hours

Battery life calculation formula:

The life of the battery B(h) in hours is equal to the total capacity of the battery Capacity(Ah) in Amps hours divided by the output current taken from the battery I(Ah) in Amps hour. Hence the battery life calculation formula will be

Battery (h) = Capacity(Ah) / I(Ah)

Also you can convert the battery life in days, months and years. Here the formula will be

Battery (day) = Capacity(Ah) / 24 x I(Ah)

Battery (month) = Capacity(Ah) / 30 x I(Ah)

Battery (year) = Capacity(Ah) / 365 x I(Ah)

Sometimes, you may do not know the output current; hence you can calculate the battery output by below formula

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Load current (Amps- Hour) = Total Load (W) / battery Voltage (volts).

I(Ah) = P(W) / V(v)

Here the load current I(Ah) in Amps hours is equal to the total load P(W) divide by the battery voltage V(V) in volts.

Hence the battery life formula can be written as,

Battery (h) = Capacity (Ah) / (P (W) / V(v))

 = V (v) x Capacity (Ah) / P (W)

The battery life is equal to the battery volts times of the battery capacity divided by the total loads.

Hence, while increasing the load, the battery life will be reduced.


Let us consider the 12 v 100 Ah battery. The battery is connected with the 60 watts bulb. Calculate the battery life.

Apply our formula,

Battery life = volts x capacity / power

 = 12 x 100 / 60.

 = 20 Hours.

Hence the battery stands up to 20 hours.



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