What is the proper technique for testing a battery with a hydrometer?
B. L., via e-mail The battery’s state of charge is determined by measuring its specific gravity, which is a measure of its concentration of sulfuric acid. The specific gravity of a battery ranges from 1.120 to 1.300, depending on its state of charge. Before testing, make sure the battery is fully charged and the electrolyte is at the proper level. If you must recharge, wait at least 30 minutes before taking the first reading. A deeply discharged battery’s electrolyte is not mixed well and will not be so until the battery begins to reach full charge (which, because of the electrolyte condition, takes a long time) and starts to gas. If you must add liquid before charging, make sure it is only distilled water, as other water most likely contains minerals and impurities that may prevent the electrochemical reaction from reaching its full potential. Draw enough electrolyte into the hydrometer barrel to allow the calibrated float to ride freely. Then read the specific gravity where the surfa
