The only present way to power a Terminator (like Arnold):

would be to have a gasoline generator on board running all the mechanisms of his body. He might run his autonomous computer activities much like a military drone through batteries but most of his power would have to come through a gasoline generator in order to power him successfully throughout the day. I'm not sure you could get enough electricity just using hydrogen powered fuel cells but that might be a possibility too. But, how would you power the weight of the structure. Terminator (Arnold Schwarzenegger's size) likely would weight at least 300 to 500 pounds and that takes a lot to move around that much weight efficiently and effectively. So, likely he would weigh being built of titanium about like a KLR 650 (388) pounds or more maybe like a Harley. And you have to have some way to move all that weight around on two legs, walking, jumping and running through almost any kind of terrain to do that.

The Arnold Terminator likely couldn't ride a horse either because he weighs too much for that but he might ride a camel or an elephant if they were big enough.