i have never heard of Fireboy and Watergirl, but i will write something nonetheless... ;^)
I think it works very well as a coordination-based puzzle game. I played both robots myself, and I had fun figuring out where they needed to climb on top of each other, where one of them had to wait, and when the other had to act somewhere else.
I honestly did not feel much pressure from the battery, but sharing the energy is a neat concept. If you expand the game, it might be worth integrating that mechanic more directly into the puzzle solutions, because it has a lot of potential.
The pixel art is charming and very well done, especially considering the short time frame. Great work!