Battery maintenance — instrument for checking electrolyte specific gravity Which instrument is used to check the specific gravity of a lead–acid battery's electrolyte (acid)?

Introduction / Context:
State-of-charge in flooded lead–acid batteries correlates with electrolyte specific gravity. A quick diagnostic requires the correct instrument that measures fluid density.

Given Data / Assumptions:

• Automotive flooded (serviceable) lead–acid battery.
• Access to electrolyte via cell caps.

Concept / Approach:
A hydrometer measures fluid specific gravity using buoyancy (float) or digital density measurement. As a battery discharges, sulphuric acid concentration decreases and water proportion increases, lowering specific gravity. Thus, hydrometer readings indicate charge level and cell health.

Step-by-Step Solution:
Draw electrolyte into the hydrometer.Read float scale to obtain specific gravity (commonly ~1.26–1.28 for fully charged at 25°C).Interpret deviations to assess state-of-charge or cell imbalance.

Verification / Alternative check:
Open-circuit voltage per cell (about 2.12 V fully charged) corroborates hydrometer readings; temperature compensation is important.

Why Other Options Are Wrong:

• Hygrometer: measures humidity of air, not liquid density.
• Anemometer: measures wind speed.
• Multimeter: measures electrical quantities (voltage/current/resistance), not specific gravity.

Common Pitfalls:
Ignoring temperature correction can mislead readings; ensure cells are not stratified before measurement.

Final Answer:
hydrometer