General Information

The most accurate means of checking the state of charge of a lead acid and/or maintenance-free battery is measuring the specific gravity of its electrolyte. This is accomplished using a good quality battery hydrometer. The hydrometer should be the hydrometer-thermometer type such as Snap-on BB4B which permits the user to adjust the observed specific gravity reading based on the temperature of the electrolyte.

The specific gravity range for state of charge is:

1.265 - 1.299 Full Charge
1.235 - 1.265 3/4 Charge
1.205 - 1.235 1/2 Charge
1.170 - 1.205 1/4 Charge
1.140 - 1.170 Barely Operable
1.110 - 1.140 Completely Discharged