SOC, short for the State of Charge, is used to describe how full a battery is. When a battery is fully charged, we can say that the SOC of this battery is 100%. SOC can be used to describe how fully the lead acid battery charged, cause lead acid battery always need to be fully charged for storage. Later nickel batteries and lithium batteries also take SOC to describe energy reserve. Here is a formula describing the relationship of SOC and DOD, that is “SOC = 100% - DOD”.