State of Charge

How to calculate the capacity or remaining power in your battery


State of charge or capacity or AH and voltage of a battery are all related. The chart below shows the correlation between the voltage of the battery and the State of Charge. This means the amount of power left in the battery. Another way of addressing this is to use Depth of Discharge but for now, let's cover off the State of Charge.

If you were to use the PC2150 as an example this battery has 100Ah capacity so if the battery is 12.50 Volts with a state of charge of 75% it would also have 75Ah capacity remaining.

You'll also note that the voltage doesn't go down to zero volts. You are doing damage to your battery below 10.5 volts and should never be left at this voltage if you want to use your battery in the future as it will quickly become sulfated.

Voltmeter Reading State of Charge
12.84 Volts or higher 100%
12.50 Volts 75%
12.18 Volts 50%
11.88 Volts 25%


Back to top