I had two 7.4v 5000mAh 40c (ProTek) batteries expand very badly and break open. Just wondering if there is a common thread here, IE- brand, maintenance, care. I'll be honest, the second battery I left in my SC10, connected to the ESC, with the power switch turned on, for about 5 days. I'm thinking that might have had something to do with the second one. Let me have it, I caused that, right??? (If I did, shouldn't a battery be able to be discharged and not "explode"??) I understand that the battery will be useless anyways for the fact of going below the 3.0 volts per cell, but shouldn't it not explode? I don't know.

The first battery has no excuse! Not plugged in, not connected, and found it exploded.

My question is, what thing/s in your experience or from what you've heard, will make a battery "explode" every time?

I think u may need to learn some lipo care. They should never be discharged below 3.1v per cell. Both your batteries need to be disposed of properly so that further damage is not caused. You're lucky you didn't burn your truck or house down. Are you using a lipo charger? If so, are you sure that you have your setting correctly?

Hi, try to read up on LIPO usage and care here:

http://www.rcgroups.com/forums/showp...99&postcount=1

http://www.rcgroups.com/forums/showthread.php?t=1287041

LIPO can vent (expand), burst and even explode if overdischarged.

You're lucky you still have a house to live in. I keep my LiPos in LiPo sacks, and then put them in a steel metal box.

You just overdischarged them below what those lipos will tolerate. Don't blame on the lipos, you are pretty much the reason. I suspect you overdischarged the other one as well. Overdischarge will cause the swelling or puffing you've seen. Some lipos will tolerate lower voltage better than others, I use 3.4v/cell as a cutoff for just this reason. Plane guys use an even higher cutoff.


You could have easily had a fire with the one you left plugged in and turned on. I'm glad you didn't hurt anyone else.

Ignorance can be a bliss but also deadly...

I have two of those packs.

One did puff up so badly that it separated the case, the other is just fine. Both were maintained properly, never discharged below 3.1V and stored with half a charge. Even though A-Main (ProTek) says you can charge at 2C I never exceeded 1.5C and normally charged at 1C.

So I sent the puffed one back to A-Main since they wanted to inspect it, a week later I had a brand new 7.4V 2S 5000mah 50C pack. The better news is that the new pack doesn't have the battery bumps on the bottom so it fits into my Ultima SC with room to spare. (maybe I should have sent both packs in ).

Just because you charge it properly, and don't go below 3.1v per cell doesn't mean its not going below 3volts per cell UNDER LOAD.

I stop running when the battery reaches 3.8v per cell and would alter my run times if I'm approaching 3.6v.

I'm aware of that. Been in this too long to neglect batteries but occasionally you do get a stinker and unfortunately there are too many LiPo stinkers out there.

Almost everyone I know has had a puffed pack or two or more. It is a fact of life with LiPos. Even the best vendors packs may puff, I think it may be related to the lunar phases.

My reply was intended for anyone checking cell voltage with no load and thinks they are doing the right thing discharging their packs to 3.1v per cell.

A cell at 3.1 volts is definitely going well below that under a 25A load.
puff the magic dragon.

That is one good reason for setting their LVC to 3.5/cell.

Pretty sure this has been discused but can't remember. With so many esc's having LVC on them now don't they read the voltage under load? If they didn't/don't wouldn't we see more of this problem with guys running to LVC all the time? (not a good idea IMO)

To the OP, glad nothing bad happened, lesson learned I hope. I'll leave it at that.

Dont leave the battery plugged in either. Even with the esc off it will still discharge the battery.

Thanks guys. I now understand (I even did before, but didn't know what the consequences could have been) not to leave a LiPo battery connected to the ESC and to turn the switch off (unplug the battery completely). I do feel lucky that nothing happened. Which leads to one other question.

So, basically, sooner or later, all LiPo batteries will "explode", if left alone long enough to discharge??? Right?

Its well documented that there is a continuous drain on batteries left plugged in and turned off with an esc. That is a sure fire way to overdischarge a lipo battery. For lipos in an RC, they must be unplugged when you put the RC away - always.

Some premium lipos are more resistant to swelling than less expensive lipos, but yes, if you put one on continuous discharge and forget it, its very likely going to puff. This puffing might be a impacted by the discharge rate - if its a trickle, the lipo might not puff, but if its a several amp load, its going to swell.

The only literal lipo explosions I've read about are due to overcharging and direct shorts where the main power wires are shorted together.