Connecting Cells in Parallel: Can This Be Done? - RC Groups
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Jan 07, 2013, 09:51 PM
AEMontoya's Avatar

Connecting Cells in Parallel: Can This Be Done?

Hi All,

I have two 4s 5300 mAh 4s lipos that are both brand new. One of them arrived with one cell completely dead (0.7V). It is beyond the warranty period (I should have checked individual cell voltages when I got them). I realize that I could try to tickle charge the dead cell using the NiCd/NimH setting on my charger, followed by finishing the charging off with the charger's lipo settings. However, I imagine that the cell has been dead since arrival (4 months ago), and that not only is it probably irrecoverable, but the original problem that caused it to die is likely to remain even if I can successfully charge it (after all, how could it have gotten discharged in the first place?).

So, I would like to combine the two packs in parallel: the 4 cells of the good battery with the 3 cells of the bad battery. In other words, the idea would be to produce one 14.8 V 9275 mAh battery (5300 + 5300(3/4)). Can this be done without too much trouble? I have already combined a 4-cell and 1-cell lipo to form a 5-cell lipo before. I have also removed cells from lipos in order to decrease overall voltage. Therefore, I think I have the technical skills to do it; but, I don't know how it can be done in theory, including dealing with the balancing leads. Any input about how this can be done or whether I should go ahead and try to revive a dead cell that's likely been dead for quite some time, and whose original loss of charge is unknown?

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Jan 08, 2013, 02:47 AM
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Roguedog's Avatar

Not going to work in parallel as the dead cell will drag down its parallel brother. In the example you gave you combined in series ending up with a 5 cell lipo for a total of 18.5 volts

If you really want to geek out on that bad battery cell you could always find another 2 or 3 cell lipo that has the same mahand size, canibolize one cell out of it, and try to replace the bad lipo cell battery in the 4cell pack. Would make a good build thread or how to thread with pics.

I found replacement lipos for my 18volt Ryobi battery packs thatt went bad on ebay. Cheeper to replace the bad lipos than to buy new battery packs.
Jan 08, 2013, 04:15 AM
Registered User
To connect in parallel you MUST have the same number of cells/overall voltage. You've got a 4S and an effective 3S. It won't work and if you try it will almost certainly kill your one good pack.

BTW this is the sort of question that's answered every day in the Batteries and Charger forum. It doesn't really fit in DIY electronics involved .

Jan 09, 2013, 11:39 PM
AEMontoya's Avatar
Okay, guys. I got it. Thanks. Sorry about posting in this section. I looked around for one on batteries, but must have missed it.
Last edited by AEMontoya; Jan 09, 2013 at 11:46 PM.

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