What is the most reliable and preferred method for determining the state of charge of a wet-cell NiCad battery?

Correct Answer: Option B — Measuring the battery voltage with a digital voltmeter during charge or discharge.

Unlike lead-acid batteries, nickel-cadmium (NiCad) electrolyte specific gravity does not change significantly with state of charge. Therefore, hydrometer readings are useless; terminal voltage measurement under load or charge using a calibrated digital voltmeter is the only reliable determination method per IEEE 45 guidelines.