Do nickel-cadmium batteries develop “charge memory” if not fully discharged?
Dear Cecil: For years I’ve heard that nickel-cadmium batteries which are not fully discharged will “develop a memory” upon recharging, and–after a time–if they are only partially used each time before recharging, eventually the full capacity of the battery will not be available. Is this true? — Hobberstad Cecil replies: It’s a myth, bud, though one with a basis in fact. Many years ago in the space program it was discovered that a computer-monitored nicad battery repeatedly discharged to exactly 25 percent capacity did develop “memory”–eventually a quarter of its charge became permanently unavailable. But this kind of thing seldom if ever occurs in earthbound applications. More commonly one sees a condition that mimics true memory, called voltage depression. In some overcharged batteries the available voltage may drop partway through the discharge cycle, spoofing a low-battery monitor (on a laptop computer, say) into indicating that the battery is low. But there’s still plenty of goo
