simple question

[maximus]

what is the most powerful battery existing (by powerful i mean by power capacity/size ratio)

[russ_watters]

Do you mean how FAST or how MUCH? Lead/acid (car) batteries can discharge VERY quickly, so they can probably supply the most wattage (but for a short time), but lithiums have the most total capacity.

Batteries are typically rated for amp or miliamp hours and they are labeled as such.