Whites TDI Beachunter additional battery?

[Pilikia]

I have a Whites TDI Beach hunter and I'm looking for an additional battery for it.
Any ideas where I can buy one? Rechargeable, not alkaline.

Thanks!

 

[Steve]

I made my own. Total cost about $25. The red battery that's on ebay for the tdi will fit into the beach hunter if you hack of the end pieces so that the compartment door will shut