Thanks Pat for all the useful info and link.

The ESC in question looks identical to mine, and in Australia too. I should probably buy another and watercool both.

I have previously used 2 x 6v x 7.2 Amp hour gel cells in series successfully with my other patrol boat that has 2 x Mabuchi 550s, so I was going to start with them, but also try some 5ah NiMH D cells as an alternative. It will be 12v with as many Amp hours that I can get to fit into the hull for the right weight.

I shall post some photos of some of my ships soon.