Originally Posted by deco

Computers can retain electric charges even when disconnected; lotsa folks don't do it now but back in the days when everyone did mods on their PCs, one would wear a static discharge band to keep from frying either oneself or one's motherboard. Car batteries too can spark whether the car is on or off; it has nothing to do with the car being on, if the battery has juice (and it has to for the car to start), there is potential for an arc from terminal to terminal or from terminal to ground. Depending where it grounded, seems pretty likely the voltage from an Xfire battery spark could zap an onboard computer or de-program a chip with programmable memory.