O2 usually isn't a problem if you have any kind of water movement, and in some cases at least, simply stirring the water around a bit will suffice. At any rate, there are pretty good battery powered air pumps that can be had that will keep the water moving enough such that O2 isn't a problem.
Heat is a problem.
If you add the water in batches, you need to balance the stress of repeated temperature changes against chilling the fish. If you have a small tank, or at least a small heat need, you theoretically could supply heat by using a car battery. If it isn't in the tank proper, and you have no way to pump water into it, then you won't have much. If you try running warm water into the tank constantly like I mentioned above, this might also suffice as a way to get rid of excess ammonia. This is, after all, the gist of how they deal with ammonia in aquaculture.