To determine the state of charge of a nickel-cadmium wet-cell storage battery during charging and discharging, what is the most reliable method?

Correct Answer: Option C — Checking the electrolyte specific gravity in the cells.

Unlike lead-acid batteries, nickel-cadmium electrolyte specific gravity remains nearly constant during charge and discharge cycles, making specific gravity useless for checking charge state. Cell voltage or amp-hour accounting must be used instead for NiCd.