The Human Battery
You are not like a battery. You are one. Not as a figure of speech — as a matter of physics.
Inside every cell you have hundreds of tiny power plants. Each one pushes charged particles across a membrane to build up a voltage, then lets them rush back through and uses that flow to make fuel. It is a battery, charging and discharging, and there are trillions of them in you right now.
The voltage is roughly 150 millivolts across a membrane about five nanometres thick. Work that out and it is near thirty million volts per metre — lightning-strike field strength, held continuously, in every mitochondrion in your body.
You carry only about sixty grams of that fuel at any moment. But you make and burn roughly your own body weight in it every day. The battery is charged and drained something like a thousand times over between breakfast and bed.
Peter Mitchell worked this out and won the Nobel Prize for it in 1978. It is not a theory and it is not new. It is simply not something anybody measures.
Four things decide how well that battery works: how well you make charge, what drains it in the background, how much you can actually spend, and what the whole thing is built from. Those four are what we test.