Hey thanks for the link. Basically the box containing the battery and reciever needs a switch. This would be a physical switch, or an electromagnetic switch. Because of the amount of water what will go over the box I was thinking of an electromagnetic switch.
That’s an good idea, I can see because these have no physical moving parts they activate at much lower power, even for the 40 amps I’d need:
https://www.aliexpress.com/item/1005005371204218.html
What I need to look into is how much power these dissipate / loose.
Great tip!
Joss