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)?
Correct Answer: hydrometer
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