A friend and I are making an underwater camera submarine. It's not motorised yet, but it mught be one day.
We haven't done much yet, but I'll document the progress.
The raspberry pi runs on 5V dc, so we need some batteries. We used cells from old drills, which are 1.2V each (x4 = 4.8V).
That last shot is the three batteries charging on a hacked computer power supply, using the (red) 5V rails from the molex connectors.