Charging from a car

[JohnK]

Hi all,
I remember reading that some people with boats on trailers use the second power socket on the tow hitch to charge the battery when towing the boat.

Does anyone know how to wire this up, is it simply a connection straight to the battery?

TIA,
John

 

[Geoffs]

Really need a split charge relay, about £2 from www.discount-towing.co.uk

 

[brianrunyard]

Need a split charge relay or blocking diode, otherwise when you start the car engine, it will try to draw current from both batteries and the cable going to the second one isn't heavy enough to take the current, at best will burn out the cable at worst will cause a fire.