Battery NiCad overheating can occur when

• A. Overcharging
• B. Undercharging
• C. Regular use
• D. Low ambient temperature

Answer: (A)

Overcharging a NiCad battery leads to overheating. When charging continues after the cell is full, the chemistry drives water in the electrolyte to decompose (electrolysis), producing hydrogen and oxygen gas. That gas buildup raises internal pressure and the continued input of current is dissipated as heat inside the cell. The combination of gas generation and energy lost as heat from the ongoing charging causes the battery to heat up, and can damage or reduce its life if repeated.

Undercharging or regular use don’t inherently cause overheating because the issue isn’t excessive charging energy being added, but rather charging beyond what the cell can safely store. Low ambient temperature tends to slow chemical reactions, which can actually reduce heat generation rather than cause overheating.