Caring for 12 volt batteries

12 Volt AGM Batteries

The name 12 volt battery is a little misleading.

When a 12 volt AGM battery reads 12 volts it is nearly flat.

When taking a reading of the state of charge (SOC) of a battery it should be done when the battery is at rest ie when there is no charge coming in to or out of the battery, otherwise a false reading may be obtained.

The reading should also be taken a couple of hours after the battery has come to rest otherwise there may be some residual effect on the reading.

Please see a suggested state of charge chart for a typical AGM battery below.

Batteries like being charged or nearly fully charged – the more they are kept fully charged the longer they will last.

Even if a battery is taken down low only a few times it could have a detrimental effect on its life.


Percent of full charge 12 Volt    DC System
100% 12.7
90% 12.6
80% 12.5
70% 12.3
60% 12.2
50% 12.1
40% 12.0
30% 11.8
20% 11.7
10% 11.6
0% <11.6