Board Thread:FAQ Board/@comment-6697950-20140113102546/@comment-6697950-20140225123319

Don't know why such a question is raised at the last episode of the Aincrad Arc, but whatever.

Quote: "To be a little more specific, disconnection from an outside source of electricity for ten minutes, being cut off from the system for more than two hours, or any attempt to: unlock, dismantle, or destroy the Nerve Gear. If any of these conditions are met, the brain destruction sequence will start."

Basically, the NerveGear must be plugged into a power source at all times to avoid brain frying. 10 minutes is an amount of time that the NerveGear can run for without a power source and still have enough power to fry a brain. Thus, by the time it does run out of power, there won't be a brain left to fry.