You won't necessarily have a bomb. If it crosses the live AC, you'll just have a loud crack as it shorts it, and the solder ball will probably be about 75% vaporized, due to the amount of current going through it. You may also trip the GFI/GFCI if that happens. Chances are slim as hell that there will be a solder ball of that size, anyways.
I'm willing to bet that Exarach's case was just a fluke incident, but it doesn't hurt to be cautious, anyways.
If anyone wants to discuss this further, we can take it to PM, or start a new thread. I don't want to hijack the thread.
As for charging batteries, you want something that will terminate the charge, when the cells are fully charged, versus constantly putting power into them, like wall-warts. That's where balancing chargers like the IMAX B6AC come in handy. You can choose your charge rate, up to 5 amps (50W maximum, so lower current, if you are charging a higher voltage battery).
As a general rule of thumb, if memory serves me correctly, 0.2 C is considered the optimum charge rate, for keeping cells healthy. As some of us know, though, that isn't always what we need. Sometimes, we need the battery charged fast (i.e. at a game, where you want it done ASAP). Thats where the smart chargers come in, and chargers like the B6 (or any charger that will allow you to use a car battery as a power source). Charge it at 1 or 2 C, and have it ready fairly quickly. NOT something to do often, unless the battery pack/manufacturer say that it is safe to charge at that rate.
~Brian
