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>Posted on 19 Jan 1996 at 21:06:51 by GILGSN@ao*.co* >From: <GILGSN@ao*.co*> >Everybody heard or experienced the memory problem with batteries when >they are not discharged and recharged properly. The battery will lose >most of it's capacity. I'm assuming we are talking about NiCd batteries. The two are very different. Memory can develop with repeated partial discharges but the cut-off level has to be extremely consistent over a large number of cycles. It's a problem in equipment with computer controlled shut-down. The solution is to randomize the shut-off point. The major reason behind the effect referred to as the NiCd memory effect is voltage depression due to _overcharging_. A few deep cycles will restore the battery to it's full capacity. However, deep discharges are risky when the battery being discharged consists of numerous cells in series. The lesser cell will enter reverse charging while the near empty cells continue to discharge. The lesser cell vents it's electrolyte as gas and with less electrolyte it has less capacity. It's an evil circle because now being a cell of less capacity it will enter reverse charging even earlier the next time the battery is run down deeply The crystalline changes to the electrodes are not very likely undone by ultrasound but ultrasound may help in breaking the Ca dendrites that grow internally and one day will short the cell. The usual trick is to burn them off with a high current but this will very likely burn a hole in the plastic separator so ultrasound might be better. The growth of dendrites can be discouraged in NiCd and NIMH batteries by charging the cells correctly and storing them cold. john
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