Help find the bad cell

[MJ]

I need to build a four cell pack for to run a com lathe. I also happen to have a toasted six cell sports pack that hopefully has 4 good cells left in it. How do I figure out which of the cells are bad and which might still be good? My available electronic tools are a Dynamite Mega Peak charger that charges at 4 amps or 1 amp and a volt-ohm meter. I can probably find other tools too, but the charger and VOM seem the most obvious.

After I make the four cell pack, can I charge it on the Mega Peak charger or is the voltage too high?

[SmokeyNDBandit]

Use the probes on the voltmeter and check each cell. They should have some sort of reading. Good ones at rest will read 1.2 etc volts. The dead ones will read 0 volts or some very low milli-volt reading. Hack those off and put the four good ones together.

Charging a four cell with the Mega Peak is perfectly fine. Use the 4-5 cell 1-Amp charge. Actually, the charger won't let you charge at the 6-7, 4-Amp cell rating...the red LED will blink instead of being solid so it's pretty foolproof.

[Railman]

There are several ways to find the bad cell. One is to totally discharge the pack & check the resistance of each cell. One should be way different than the others. They must all be in the same state of charge for this to work though. The other is to charge the pack & constantly check the temp of each cell. The bad cell should be a lot hotter than the others. I have used both of these teqniques with good luck. Good luck. ;)

[MJ]

Thanks of the quick reply. I’ll try it out.

[MJ]

All three of the tests worked and all three of them pointed to the same bad cell. Thanks again. :D