My question is very hypothetical. I've read that human brain consumes about 400-500 calories a day on average. Imagine you could somehow attach a device to body

My question is very hypothetical. I've read that human brain consumes about 400-500 calories a day on average. Imagine you could somehow attach a device to body that could burn another 1000 calories. [and probably convert it to heat - forget about burning your skin and infections for now] Do we have that kind of interface? Can we power an implant using energy stored in fat cells?