Battery State of Charge (SOC) is one of the most common things that our customers ask us about. How do we know when our battery is fully charged?
Let’s begin by defining what SOC means. A battery’s State of Charge measures the available capacity of the battery, expressed as a percentage. A fully charged battery is 100% .
You can measure State of Charge 2 ways. You can measure the voltage from the battery terminals by using a volt meter. This is the most common and easiest way. An alternative way, which you can use for a flooded (not sealed) battery is to use a hydrometer to measure the specific gravity of the electroylyte.
The SOC differs depending on the battery chemistry.
State of Charge for a 12 Volt flooded (wet) Battery
Percentage of Charge
12 Volt Battery Voltage
Specific Gravity
100%
12.7
1.265
90%
12.58
1.249
80%
12.46
1.233
70%
12.36
1.218
60%
12.28
1.204
50%
12.2
1.190
40%
12.12
1.176
30%
12.04
1.162
20%
11.98
1.148
10%
11.94
1.134
0%
11.9
1.120
State of Charge for a 12 Volt AGM (sealed) Battery
