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 |