[MadMax]

I'm really looking forward to carrying LiPo's in the nearish future. However there are a few technical hurdles to overcome before they could be really wide user friendly:

A circuit needs to be included to protect the user from overdischarging their LiPo as they get significantly damaged if you discharge them too deeply. The same goes for overcurrent draw. Protection circuits are available for the r/c plane market. I think they're light (plane flyers are weight conscious) but I don't know if they're small enough to shoehorn into AEGs.

Wow, those cells you linked to are good for 20C?! That's a whopping 66A for that 3300mAh pack. Hobby grade LiPo has progressed very fast. When I set up my P90, I think my packs were rated for only 15C. My packs are individually rated for only 22.5A which was a bit too low for an upgrade spring setup so I went with parallel packs for 45A current draw and high total capacity (3000mAh). In lieu of a proper protection cct I fully charge my batteries before a game. I've never come close to running out a 2400mAh NiCd 9.6v pack so I figured I'd never overdischarge my twin packs at 3000mAh. I play with std caps which also limits my lead trigger (you should see how fast I sneeze off a lowcap at 11.1v!).

As to catestrophic failure, I think LiPo has progressed pretty far from the days of burning laptops. Luckily for R/C, the usefullness of LiPo has made it also the preferred storage for a lot of consumer devices. Cellphones, laptops, Ipods all depend on LiPo so cell manufacturers have had to keep things safe.

I've tried to keep a bit of an eye on LiPo as I've been looking to include them in several products that I was designing. It appears that many of the early failures in LiPo were due to manufacturing defects. Thin spots in the battery windings are prone to overheating and developing breaches which allow an exothermic reaction. Also burrs or other sharp metal contamination from the outside during manufacture can later penetrate the separator in the battery piles and cause a similar failure. Failure of batteries with defects would occur if the charger overcharged or the battery was supplying a lot of current. Both cases would cause the pack to heat up and fail because the weakened separator would melt. Failures could also be caused by mechanical damage (say if you severly struck or crushed a cell) which could force a burr through the separator or even a piece of the casing if it sheared.

In any case, manufacturing techniques have improved significantly. Now exothermic cell failures are down to about one in a million in about 5 months of pack life. The severety of cell failures has become significantly less because of design changes. I think manufactures are aware of the increase in field failures from the introduction of sharp contaminants (burrs) or defective separators so they've tightened QC. I don't know how they've reduced the exciting factor in failures. Perhaps a change in composition like a fire retardant paste or a suspension of inert particles which retard oxidation if they're heated significantly.

About two years ago I was pursuing a product which was to use a LiPo for a head mounted device. I was concerned about the safety issues of a head mounted battery so I did do some crude testing on some LiPo packs. I could not get them to fail in an exciting manner with significant abuse.

First try was to short cct a fully charged pack. One cell failed first but not in an firery exothermic manner. On close inspection it looked like a single shot fusing feature failed before the cell could overheat. The connection to the outer terminals is not a huge heavy chunk of metal. It was a smallish conductor apparently designed to fry so one could not subject the cell to a prolonged short cct.

I tried a crushing test on an undamaged cell by mashing it with a mini sledge hammer on a concrete floor. Crude, but I figured that if the battery was mounted to someone's head, a sledge hammer blow would cause more damage to the user than the battery getting mashed so it was a pretty severe worst case scenario. Anyways the cell got a bit on the hot side (I'm guessing around 70C which is hot to the touch, about as hot as household hot water), but it did not burst into flames. I guess what would have happened would the the user would be knocked unconscious, suffer some brain damage from the steel hammer blow and have a stingy burn on a massive bruise if they woke up.

Last test (only one cell left at that point) penetration test. I held a nail with a pair of pliers and hammered it through the side of the cell. I had to saddle the cell into a groove in the floor so it wouldn't roll around and I had to ding the side to set the nail. Samish kind of exotherimic failure as the crush test. Got hot, but still no fire to my disappointment. If the nail didn't go clearly thru the battery, you'd have time to remove my head accessory and kick the shit out of the guy with the nailgun before getting a burn on your head from the cell heating up. Heck, hold him down and burn him with the cell.

The cells leaked some pretty caustic stuff (stings the hands), but nothing worse than what I've found in NiCds which is also pretty alkaline. Cadmium is also toxic and a cumulative poison so I didn't consider the leaking issues with LiPo significantly more dangerous than NiCd.

I'm not sure if LiPo has ever had a history of exploding. It's probably an exaggeration of the spectre of a laptop causing a fire in an airplane.

I do have a bit of concern leaving a LiPo unsupervised while charging it. I slow charge them overnight so I sleep better if I put the battery into a steel ammo box while it charges. Pictures of burned LiPos don't show the thin casings melted down so I'm pretty sure they wouldn't melt through my steel ammo box if they burned up.