When a battery is being charged, you will get a higher voltage reading than you would find at rest. Most renewable energy charging systems will charge a battery until the battery reaches 14.5 volts and then will automatically shut off. The battery voltage will drop slowly. The most accurate way to check the true charge state of a battery is with a hydrometer. A specific gravity of 1.260 in a lead acid battery means it is fully charged. As a battery discharges it will fall to 1.120 when discharged. The ratings are at 77F. If the temperature is lower than 77F then the specific gravity will be inflated. Premium hydrometers will have a temperature and give you a compensation factor.
Correction factors: 130 degrees F +0020 120 degrees F +0016 110 degrees F +0012 100 degrees F +0008 90 degrees F +0004 80 degrees F 0000 70 degrees F -0004 60 degrees F -0008 50 degrees F -0012 40 degrees F -0016 30 degrees F -0020
Percent charge Voltage 100% 12.60 75% 12.35 50% 12.15 25% 11.95 discharged 11.85 or below
Offered by Steve.