LiPo batteries = DANGER

I believe the danger of the hobby LiPo batteries is underestimated.  The batteries in laptops and other consumer equipment is not designed for very high currents (discharge rates), but the batteries used in electric-power models are.  When you see a rating of "30C", it means that the batteries can output 30 times the amp-hour rating (which is milliamp/hour divided by 1000).  So, if you have a 3000mAH battery, with a 20C rating, that means it can output 3A X 20 = 60Amps on a short-term basis - but that is their LOAD rating.  They can output several HUNDRED amps during a short-circuit condition.

Since commercial batteries (like for laptops and phones) are not required to produce very high output currents, the cells are designed differently and they usually cannot deliver huge currents - even during short-circuits. The cells are usually small (a bit bigger than AA size) and are arranged in a series-parallel arrangement to produce the required current and voltage.  The fact that each cell is not too large means that a catastrophic failure in one cell is not likely to produce enough heat to cause serious damage.  Also, laptop and phone batteries have a fusible link that blows if a cell shorts or the temperature gets too high. This keeps the energy from the adjacent cells from feeding power INTO a shorted or overheated cell, further decreasing the risk of fire or explosion.

Hobby batteries have NONE of the protection mechanisms mentioned above. The cells are usually put in series only, which means that every cell must put out 100% of the output current.  This requires a large cell. There are no fuses, no temperature limits, no "smarts" of any kind.

A charge cycle is especially dangerous. The material inside the battery actually expands with time - which is why older batteries get that "pillow" look.  Sometimes the insulator which separates the (+) and (-) plates inside the cell breaks down and the cell shorts. At that time, the full output current capability of the cell appears across its internal resistance.  My Turnigy charger has an internal resistance tester, and I find that most cells have an internal resistance of  0.010 ohms (10 milli-ohms).  If a cell has a voltage of 4V, then 4V across 10 milliohms = 400A.  400A at 4V = 1600 Watts!!  That heats the battery up within seconds. Note that this sequence occurs even if the charger stops immediately when the short is detected!  There is NO WAY to stop this.

And let us not forget that lithium (and each cell has a lot of it), is reactive.  It burns!  The end result is a very, very nasty fire with flames shooting out of the battery for several feet.  Anything nearby WILL catch fire if it is at all flammable.

But is this likely?  YES!!!  I have had this happen TWICE.  I was not charging in an ammo can, but this morning I had the battery on the charger on my concrete garage floor.  I heard a POP, and within seconds, flames shot out of the battery by more than 3 feet!  The bottom line is NEVER, NEVER, NEVER charge a battery in anything that is flammable - or within 10 feet of anything that is flammable.  I normally charge batteries in a metal "AMMO" can, and I'm going to get a second where I store charged batteries. I'm not certain that a battery sitting by itself, not on the charger will not do the same thing.

I do know that if I charge a battery in an ammo can with a bunch of other batteries, ALL of them will be destroyed if one goes up in flames. I don't know if the lack of oxygen will help quench the flames or not - but I'm not going to test any theories.  As far as I'm concerned, the only safe approach is to charge in one ammo box and store in another.