Hi TJ, RE: RX battery
Any 4 or 5 cell (4.8 or 6V) NiMh of 1000mAh up will do. Use the biggest one you can without upsetting the boat's trim or reducing it's performance / planing etc.
BUT: don't forget to disconnect the red wires between your ESCs and RX to disconnect the BECs in the mTroniks speed controller
Also check that your RX and mixer
module etc can handle 6V+!
If not use the 4 cell pack.
A fully charged NiMh will be significantly above 6V.
Some modules; e.g. Action Electronics / Component Shop don't like that 😡 Alternatives are, esp if you need to save weight,
1 use ONE of the red BEC leads from ESC to RX, e.g. the centre one, and disconnect the other two,
2 Use a separate 5V UBEC module to syphon power off the drive battery
for the RX, AND disconnect all three red BEC wires from the ESCs.
Cheers, Doug 😎