As the title says, my lipo puffed up while storing.

Lipo is 5000 mah 25c. Never have I ever drained it down below 2500 mah. Pack is fairly new with about 15 cycles. Yes, it's always balance charged and yes it's not stored fully charged.....mainly at 7.8v. No I don't store it in the warm or cold place, just at room temperature. Run the pack on my 2wd buggy. Speedpassion ESC and 7.5 motor. Normal use...never abused, ran my car indoor. Took the battery out last week to prepare for my race meeting and noticed the battery swelled up badly. Yes, my charger is a good quality one.

What could have happened

I would like to hear what other people have to say about this too. I have had the same thing happen to me twice. I just chalked it up to bad batteries and disposed of them. But, I do regularly check my stored LiPos now to make sure none are puffing.

your supposed to store lipos at 80%...

7.8v isn't horridly high...
Mine sit around 7.4v.
Has the pack taken any hard hits in the past?

SMC?

How long was the pack in storage?

SMC recommends 6.6 volts for a 2 cell. I'm sorry to hear about that.

Aren't the 'store' functions that some chargers have generally around 7.6~7.7v for a 2s? The Orion I have is 7.7v. Supposedly around 50% I thought?

That's about what I have been doing for 2 years or so, knock on wood so far....

I went out of the country and left 7 lipos, 2S and 3S stored very precisely at 50%. I'd planned on being gone for 4 to 6 weeks. Was gone for almost 11weeks. All of them puffed a cell and it was the cell that was positioned up as they were sitting, ie the top cell. This was in spring, wife was still home, we keep temp at 77-79F with a humidity at a comfortable level, 45-55%. They'd never been run hot. The puffed cells were over 3v, so I was at a loss to understand why it happened.

I never encountered a rational explanation for it either. These were gen 1 lipos and built with some kind of hard, white encapsulation on the end with the tabs, I could'nt even salvage the remaining good cells. I had well over 100cycles on them so they def were not new. I use 80% for storage and weekly ck all my lipos with a dvm.

What method did you use?

The top cell thing sure is weird.

I have a couple older mostly unused 2s packs that have sat well over 11 weeks more than once I'm sure, stored at ~7.6v. So far no problems.

This was before I had a charger that you could simply set the desired storage %'age.

I fully charged them using my Ice charger, then discharged each. I discharged 50% of the rated capacity. This is back in 2004 and that was the recommended way to handle storage at the time. Def not the way I'd do it today.

I've wondered if I had placed them on their side if it would have made any diff....or just wound up with both cells puffed.

Puffing happens on over discharge. If everything you say is accurate, then there are really only two possibilities:

1. One or more cells in parallel is bad.
2. One or more cells in parallel lost connection.

If a cell is bad or disconnected, that cell group will have far less capacity than the other group in series and will puff up when you pull it down below 3 volts -- your esc will not know to cut off if the other cell group is still doing well, keeping the voltage of the entire pack higher than the cutoff.

I’ve seen your story several times, always wondered…my condolences by the way, all of you guys included. First thought is maybe they weren’t capable of rated capacity, so you were really below 50%. But then as noted SMC apparently recommends a fairly low storage level…not sure for how long though, they are supposed to hold charge quite well, low self discharge. At the risk of flaming the faithful, (not my intention) there does seem to be a lot of SMC puffing stories lately. Related maybe?

Could it be an early generation thing? They certainly have/are improving in many respects. There were a lot of horror stories a few years ago it seems.

I store my SMC packs at around 7.6-7.8 volts. I have 3 packs and charge all of them before my races and run one per race. I come off the track and use between 900-1200mAh depending on how much practice I take before the race. But I store them that way for only about 2 days before I go to the track again to race.

Nick

6.6 sounds way too low to me...........