Open circuit voltage State-of-Charge in % of a 12V flooded lead acid battery.
Test the battery at room temperature. Allow 4-8 hour of rest after charge or discharge.
12.65 Volts = 100%
12.45 Volts = 75%
12.24 Volts = 50%
12.06 Volts = 25%
11.89 Volts or less Discharged.
Use a 1 or 2 Amp Automatic Trickle Type Battery Charger.