From the movie, can it be deciphered, where the alternative power source from the T-800 was located? It does show a schematic on the camera. Any further insight on this?
Nothing useful, I'm afraid. The schematic shows an "Aux Batt" (presumably an Auxiliary Battery) providing "reserve power" but no indication of where it's actually located. Given the fact that it's positioned on the blueprint next to a CPU cluster, I'd guess it somewhere inside the head but who the heck knows?
Oh, and the novelisation is no help either.
"Uncle Bob" used the thermal energy generated by the smelter and accumulated in its internal heat sinks to reboot. A temporary measure to stay "alive", at best, and have a last shot at the T-1000. It worked...
Not actually explained in the movie, but the T2 Extreme DVD text commentary says:
Terminator drew upon the potential energy in his heat sinks to jump start his internal systems since his main power cell was ruptured and discharged by T-1000’s attack"