How can the state-of-charge of a nickel-cadmium battery be determined?

• A. By the level of the electrolyte
• B. By measuring the specific gravity of the electrolyte
• C. By a measured discharge
• D. By the terminal voltage under open-circuit conditions

Answer: (C)

For nickel-cadmium batteries, the most reliable way to judge how much charge is left is to see how much energy has actually been used. A measured discharge directly tells you how many amp-hours have been drawn from the cell, and you can compare that to the rated capacity to determine the remaining state of charge.

Voltage alone isn’t a dependable indicator for NiCd—the terminal voltage changes little as the charge level varies, and factors like temperature and surface charge after charging can mask the true state of charge. Reading the electrolyte level or electrolyte specific gravity isn’t practical or meaningful for sealed NiCd cells, where such indicators aren’t accessible or reliably correlated with SOC.