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I accidentally short-circuited LiPo battery 7.4 V 2200 mAh 35 C. I measured the pack's overall voltage, but multimeter showed nothing. I also measured the individual cell voltages (via the balance tap plug) and only one cell showed 3.85 V.

Is this a mark that the other cell is totally dead or is there a chance of cables got unsoldered inside the battery, during the short-circuit? What should be my next steps?

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You should really get rid of the whole pack and don't absolutely try to charge it. These kind of batteries have very large flat metal pads soldered to a big pcb and it seems very unlikely to me that something fall off: your cells are probably both dead. You might carefully try to rip off the heat-shrink enclosing and carefully desolder the maybe-but-not-so-much alive cell. Then you will need to charge it, but again, this is a bad idea. If I had to do such a thing I'd do it outside, placing the battery in a fire-proof bag and I'd monitor it's temperature constantly. But I would not do that. That's 20$ on hobbyking or whatever and in my opinion it's not worth the risk ad all.

What are you going to power with the single cell anyway?

Addendum: with "get rid" I mean "properly dispose". LiPo batteries contain nasty chemicals and should absolutely not thrown like common garbage. Apart from the pollution that would derive from such an action you would also endanger the garbage collectors.

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    \$\begingroup\$ Serious +1 on the warnings. LiPo's get temperamental when they are charged or discharged out of spec. They store a lot of power and they like to let it all out at once! We had products with 3 Li+ cells that were embedded in asphalt. When we were removing them (with a jackhammer), we pierced a cell. Impressive white explosion, surprisingly large! Quite an unpleasant surprise :) \$\endgroup\$ – bitsmack May 12 '14 at 22:18
  • \$\begingroup\$ @Vladimir Cravero Do you know what nasty chemicals are in the LiPo batteries that need to be properly recycled? I was under the impression that the Lithium batteries in general were one of the more environmentally friendly batteries and the lead acid and nickel cadmium were the bad ones. \$\endgroup\$ – Filek May 13 '14 at 7:52
  • \$\begingroup\$ They are better than them but they need a sort of treatment before you can dispose of them, salty water if I remember right. \$\endgroup\$ – Vladimir Cravero May 13 '14 at 7:58
  • \$\begingroup\$ @Vladimir Cravero Yes, I heard of the salt water, but someone told me it was to "get rid of any remaining charge in the battery" Doesn't seem to be a lot of good info on the lithium battery and recycling. Where I live in Canada I am certain that you are still allowed to throw lithium away. \$\endgroup\$ – Filek May 13 '14 at 17:40
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Is your battery pack protected by some sort of battery management system or PCB? If so, it may have kicked in and "protected" your cells to some extent. I have taken apart Li-ion battery packs that read very low voltages or even zero voltage, but after removing the PCB, and VERY CAREFULLY disassembling the pack into its individual cells, the individual cells had a normal voltage and charged and worked just fine.

Can you measure the individual cells directly and not via the balancing wires? Although now that I think about it, the balancing wire measurements that you took should bypass the PCB so it is not a good sign that you got a reading of 0.

Edit: Upon further thinking I realize that the balancing wire could have one of its leads attached to the PCB (either the positive or the negative balancing wire) and if the PCB has kicked in and blocking access to the cell, it will read 0

How long was the pack short circuited? If it was only a brief period (a couple of seconds or less), then I would be suspicious of your reading of 0 volts, especially given that the other cell has a normal voltage reading. Was the pack old and near the end of its life anyways?

The safe thing to do is to recycle the battery and get a new one as li-ion are dangerous to play with!

BUT.... if the protection circuit has just kicked in then putting it in the charger for a few seconds might "wake it up". My understanding however, is that most protection circuits that kick in for short circuits, usually "wake up, or unlock" shortly after the circuit is no longer shorted. BE SAFE. Good Luck.

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  • \$\begingroup\$ I'm pretty sure he's speaking of an high power RC model battery pack, his in particular can probably source up to 77A conitinuosly, so I doubt there's a built in protection circuit. \$\endgroup\$ – Vladimir Cravero May 13 '14 at 10:07
  • \$\begingroup\$ @Filek +1 for helpful advice. \$\endgroup\$ – dempap May 13 '14 at 11:34
  • \$\begingroup\$ wow 77amps continuously is a lot. \$\endgroup\$ – Filek May 13 '14 at 17:38

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