I believe I’ve been taking care of my 1S and 2S batteries, but after a few of them have recently puffed, I’m confused.

I charge both battery types with an iCharger at 10amps.
Batteries are high quality SMC, EAMotorsports, Orca, IP, and Thunderpower.
I run 1/12 stock (13.5) and TC (13.5 boosted).
I always balance charge and storage charge when finished.
They are usually stored in my pit room (it can get about 35*C or 95*F).

Question #1
What causes puffing and what can be done to prevent it?

Question #2
When they do puff, how bad is bad (assuming the case hasn’t cracked open yet)?

What is your battery maintenance strategy?

Usually it's over discharge or heat that will puff them. In my experience. Even the highest quality cells, trinity, thunderpower, smc will puff especially in a short course truck or e buggy.

Things I can think of that contribute to or cause puffing in LiPo batteries:

-Storing for more than a few hours at, or near, full capacity.
-Very high discharge rates, especially on lower C-rating batteries.
-Over-charging (going over 8.40V on 2S, for example).

Very simple for me:

Always balance charge at 1C.
Never keep them in full charge state for more than 30min.
Only discharge to about 3.80-3.83v, goes back up to 3.85v range when I put them away.

So far, so good. I follow all of the above rules.

Would a change in humidity where the batteries are stored cause puffing?

Humidity, I don't think is a major factor in Lithium-based battery performance, though I suspect low humidity is a good thing since we're dealing with electronics.

Leaving batteries in high ambient temperatures (110F+?) will cause damage over time. More damage will be done based on how full the pack was and how long it was exposed to high temps.

Attempting to charge a battery that is at freezing temps will damage the anode and permanently increase resistance in the battery.

I acquired some batteries from my brother. 2 are good but one is puffed pretty bad. It hasn't cracked the case but is very visibly bulged out. Is there any way to reduce the puffing and is it still safe to use?

I'm interested in peoples opinion on this as well. I have two 2s 6500mah Reedy packs that are about 1.5 years old but with only 30-40 cycles on them. I always storage charge them and will periodically when not used for a while. The are puffed fairly badly but the case is not broken. The IR on my Hyperion charge reads as 3m ohms.
I am nervous about using them.
Any thoughts?

Here are some good notes on the chemical reactions that are taking place inside a Lipo that cause swelling: http://barnson.org/node/1842

Basically, they are still fine unless they are in danger of rupturing or being punctured, or as long as they are still taking a charge at a reasonable rate. Puffed batteries still perform, it's just that their internal resistance is likely to be much higher than a healthy battery. This leads to a lack of power production (decreased efficiency) and increased charge times.

I'd say if you've got a battery with a cell that never charges full during a balance, it might be time to consider retiring it. If you're running an extremely powerful motor you may need to consider replacement as well-- the harder you stress a failing battery the more damage is done internally and the chance of a fire/explosion increases.

Use your head, if it is hard to charge or looks like it is going to pop, discharge it and get rid of it.

No there isn't.

My 2 cents....I have been using Lipo's in planes since they came out. Cars just a couple of years.
I have never puffed a lipo. I have used just about every major brand.
Leaving a lipo at full charge longer than 30 minutes can puff one ....that is complete bullshit.
In the early days I did not even know about discharge. I had a few cell pro's that I left at full charge for weeks. Never puffed.
Even today I charge my lipos 4 to 8 hours before racing....no puffing.
Flying a 4s Stryker plane and the battery was very warm on landing no puffing.
I think I pushing this battery pretty hard.
I Always balance charge at 1c.....
Maybe that is the answer.
My thought is if you need to charge at a really fast rate, why not just buy another battery to swap out.
So in my opinion it has to be either to high of a charge rate or running the battery to low ...

I have a ton of lipos for our track rental cars. They are the $17 zippys. We use these packs everyday and have for almost a year. I would say on an average week they get charge appox 50 times. I charge them at a little over 1c, 5 amps max. They get balanced once a week. I have noticed a drop in performance and run time, but none of them have puffed or gone bad. I also have used other brands, smc, protek, losi, trackpower, thunderpower, racers edge, Rev tech, all the same way, and yes some of them have puffed and cracked the case. We have replaced them. I have never noticed a pack that puffs from charging. For example my 3's lipo I use in my 1/8 LM. I run it about once a week, maybe 2 packs. It is at approx 130 degrees off the track, it has started puffing now that I am pushing it harder and running it completely down. I charge at safe levels and have not had any issues, but running packs until hot and completely empty, mine hace all puffed and now lack performance.

I can assure you that the chemical reaction that is producing Oxygen inside your cells is more active the more full the pack is. 30 minutes (one time) to puff, absolutely not. There is such a thing as cumulative damage, though.

Good for you? Why would you suggest other people treat their gear poorly though?

I run Ebuggy on 4S, battery gets up to 105F in the car. Doesn't puff-- not being overdischarged for its C-rating. Try shorting one of your batteries out and see if it puffs...

No, it isn't.

Well that's a fine opinion but I suggest you try to back some of your assertions up with a little science.

Just stating my experience's over the past 9 years of using lipo's.
So I am sorry if I offended your expertise on the science on lipo's.....you must surely be more intelligent than I.......