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Old 8th August 2023 | 23:41
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MechEngr
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It's a different problem than NiCds - in laptops there is a chip that constantly tries to estimate "state of charge" and it uses voltage and current in and current out to make that estimate. If the voltage remains relatively constant, as it does when kept charged then any errors in current in vs current out accumulate and the chip will tend to report the wrong battery life. Running the battery down to the minimum voltage resets the charge monitoring data.

There is a claim of "memory effect" for other cells but any series battery pack that doesn't have active voltage balancing can have problems. At some point one cell will be the slacker. It will drop in voltage a bit more than the others and won't get fully charged with the rest. The remainder might end up overcharged, with a rapid drop-off that looks like "memory" but an examination will show one or more cells is suffering.

I saw a bunch of replaceable NiMH AAs used in a camera by some coworkers. The camera would die after short use from a "full charge" and they'd slam them all back on the dumb charger. They came off hot to the touch. One of the cells was under 0.5 V out of a possible 1.2V. Tossed that one and grab a spare and suddenly the camera works again. Yay! In laptops it's tougher to detect as there is usually a sensor to keep the temp of the pack down instead of bursting into flames.
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