No battery, of any sort, should be short circuited, disposed of in a fire, or exposed to extreme heat or water. No rechargeable battery should be over charged or excessively drained, and it is always a good idea to be watchful and present when recharging any battery, not just li-ions.

Avoid the cheap junk and li-ions without protection circuits. Candlepower forum is a good starting point source for information. The payoff is that you will have a lot more light available, either lower light level for a much longer time, or much more light for a fairly short period.

I have two 18650 lights (Nitecore and Zebralight). They weren't cheap but they are very capable and versatile. I also have a bunch of AA and AAA lights, all using rechargeables. With a reasonable amount of attention, my portable light needs are well met.