How many batteries would you have to implant? And the wiring would be a bitch.
Don’t fall in the pool.
Why bother with batteries? Why not use tiny thermocouples (or is it thermistors?) and run them off of body heat?
Hmmm… could you get hypothermia from them sucking away your heat?
That would take an awful lot of LEDs. They keep making them smaller, more efficient and requiring less power.
Glow your fat away!