What is the primary purpose of a hydrometer in battery maintenance?

• A. To measure the specific gravity of the electrolyte
• B. To measure the battery voltage
• C. To check battery temperature
• D. To read the battery chemical composition

Answer: (A)

In battery maintenance, the hydrometer is used to measure the electrolyte’s specific gravity. The gravity reflects how concentrated the sulfuric acid is in the electrolyte, which changes as the battery charges and discharges. A higher specific gravity means more acid and a higher state of charge, while a lower gravity indicates a more discharged cell or potential weakness. By taking readings from each cell, you can assess overall health and identify cells that aren’t charging properly. This is different from measuring voltage, which tells you electrical potential, or temperature, which can affect readings but isn’t what the hydrometer measures. The hydrometer doesn’t read chemical composition directly; it gauges density, which correlates with charge state.