Re: 41C battery pack HP82120 Message #2 Posted by Yani on 10 Dec 2001, 4:01 p.m., in response to message #1 by john robinson
Hmm... In other circumstances I would say it sounded like shorted cells. This is very common where fine hair like wires grow inside the cells between the electrodes and short out the negative and positive electrodes. It usually shows up as a decrease in 1.2V on the overall battery pack. In this instance it looks like two cells may have developed shorts.
Calculators are particularly susceptable to this since they are very low current devices. The high currents in childrens toys for instance do not allow the growth of these hairs. I have seen these hairs grow in thin air with no more than a low voltage between a steel plate and components seperated by about 1/2 and inch.
To test this check each individual cell. The good cells should be about 1.2V and the dead cells should be 0V.
If this is the case there are two alternatives. Replace the cells or "thump" thenm with a very high current to burn off the hairs.
If you replace the cells replace them all and use better quality cells. Any 1/2 N type should suffice. I would use NiMH. They are far better than NiCd. To thump the cells use a high current source (a car battery is good) to generate several amps for a second or so. It does not take long. Remember positive to positive and negative to negative. DO NOT I repeat DO NOT LEAVE THE CELL CONNECTED TO THE CURRENT SOURCE FOR MORE THAN A COUPLE OF SECONDS otherwise the cell will EXPLODE!!!!!!!
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