What is battery life? – Definition, Formula And Example


What is battery life?

“Battery life” is the amount of time a device runs before it needs to be recharged. “Battery lifespan” is the amount of time a battery lasts until it needs to be replaced. One factor affecting battery life and lifespan is the mix of things you do with your device.

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

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 24 v 200 Ah battery. The battery is connected with the 60 watts bulb. Calculate the battery life.

Apply our formula,

Battery life = volts x capacity / power

 = 24 x 200 / 60.

 = 80 Hours.

Hence the battery stands up to 80 hours.

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