How do NiCad batteries fail?
Marty Goodman writes: In answer to your question about how NiCd batteries fail: My understanding is that principly they fail in one of two ways: The first is gradual. Their capacity gradually decreases bit by bit with each recharge over time, until it drops below a level that’s acceptable for the application in question. Arbitrarily that level is often listed as 85% of original capacity, but of course if you are in an application where the batteries when charged have two or three times the capacity you need the definition of “dead” may be more generous. This is seldom the case for night bicycle lighting, however, where we usually want nearly full capacity for issues of run time and weight. There the 85% rule probably is more or less correct. However, NiCd batteries also fail in a second way: They grow “dentrites” internally, which internally short out the battery. Dendrites gradually grow, but it’s only when they actually complete the internal short circuit that you notice them. Thus,
