I wonder what kind of power source the Terminators would have as a back-up, where would it be located and how big would it be/how long would it last?
http://terminator.wikia.com/wiki/Series_800
From the page:
"If disabled, the T-800 is able to re-route its systems to a secondary, alternate power source, thus bypassing any severed connections, damaged circuits, or internal impairment. The 800 Series also has redundant backup hydraulic systems. Therefore, it is imperative that Resistance members determine that any T-800’s are totally incapacitated in combat, lest the units are able to revive themselves and continue battle or pursuit of their target."
And...
"In its final fight with the T-1000, it received heavy abuse from the superior machine, including repetitive blunt trauma to the head which caused enough hydrostatic shock to render the machine immobile for a short time. It fell to the floor and was unable (or unwilling) to exert the energy required to get back up. The T-1000 then drove the same metal rod into its back, twisting and bending the back plating to allow it to drive the rod into its primary power cell, disabling it. The T-800 was able to use heat sinks to revive itself, however; and absorbed enough thermal power to remove the rod, grab its weapon, and crawl onto an upward conveyor belt. It was later able to get back to its feet and walk with assistance from John Connor."
While this doesn't specifically state what kind of power source is used, it can be inferred that it's probably a capacitor that holds a charge based on a heat to electricity type of conversion, similar to an iguana or other cold-blooded animal that suns itself to stay warm and active. This could logically be a means by which Skynet wanted to make them non-dependent on nuclear power, "evolving" them into geothermal-powered machines.
It also makes sense from a logistics standpoint. If your entire population is dependent on one specific thing to survive, all the enemy has to do to win is deprive you of that one thing. By making Terminators capable of using multiple power sources, especially one that you just cannot get rid of, Skynet will essentially be unstoppable. Had they had more time to perfect the process before Connor and Co. destroyed the mainframe and defeated Skynet, Humanity would have been doomed no matter how well they fought back.
