A built-in hydrometer indicator showing green on a battery usually indicates the battery is fully charged.

• A. Fully charged
• B. Charging
• C. Needs water
• D. Faulty

Answer: (A)

A built-in hydrometer on a flooded lead‑acid battery uses the electrolyte’s density to show how charged the battery is. When the indicator shows green, it means the electrolyte density is in the range associated with a fully charged cell, so the battery is considered fully charged. Temperature can affect density, so some indicators account for that, but the green signal generally corresponds to a full charge. It wouldn’t indicate that the battery is actively charging or that it needs water, and a fault would usually show an abnormal color or a lack of a reliable reading.