I just want to point out not all go to the lengths Tom does when it comes to battery safety (see above). Not saying he's wrong to do that, but I believe there are reasonable safeguards already built in, and used in a reasonable manner, batteries and chargers supplied with production bikes can be used safely as is. There's a very low chance of fire when used according to the owner's manual.
The guys having issues are messing with home made battery packs, charging multiple packs at a time, or otherwise using "creative" methods/technology. If you want to try something like that, cautions are a darn good idea, just in case your ideas are not.....