Originally posted by Bob 256 Ditto on that. Only use the appropriate type charger for lithium ion batteries (and advisably for NiMH batteries too).
One gadget I found handy is a small 12V to 110VAC converter (plugs into a cigarette lighter and gives 100W of AC power). When on the road, I can plug my K-1 charger into it and charge my spare K-1 battery. It also allows me to charge the K-1 battery from any 12V source without worrying about the complexities of directly charging a lithium ion cell (a cigarette adapter with clip leads is also available). Good to have in your gadget bag.
Still not much help though if you forgot the K-1 battery charger.
The power output from those small converters is very dirty. I'm not clear if they actually provide clean enough power to not harm the Li-Ion batteries. There are many forums on power tools and water craft that indicate that inverters do not work well in the long run for batteries. The square wave most produce is not a great source for DC output for things expecting a sine wave.