Bill Daniels wrote:
Yes, in EXTREMELY rare occasions there can be a problem - usually a product
recall for a 'warm' device with a wiring problem. A shorted 7AH SLA won't
be pretty either. The safety issue is an old story that has been almost
completely overcome with new designs.

Most "Li-ion" batteries contain Li-polymer cells these days. Having
witnessed the spectacular results of incorrectly charging a 6 cell model
airplane Li-poly battery pack (luckily, outdoors on concrete), I can
easily see Tom's point. I've found a video (complete with kewl music),
the batteries we'd use would be about 5 or 10 times this size:

http://www.helihobby.com/videos/LithiumBattery.wmv

A battery pack produced by a reputable manufacturer with a matched
charger, and proper short circuit protection, is probably safe. But, if
people start lashing up Li-poly packs and chargers the way we do with
SLAs, sooner or later someone will regret it. NiMH is much safer when
mishandled, and still offers an improvement in size/capacity over SLA...

Marc