Batteries going flat (1 Viewer)

[MitchandJenny]

engine battery went flat. Took iT off and tested iT, iT was OK after a charge. The red light on the dash stayed on flashing as normal. But are the two batteries connected permanent ? I turned Some habitation lights on and the engine battery showd a drop. Why should this be ?
Help please.

 

[pappajohn]

If you have a conventional split charge relay it MAY be the contacts have welded in the closed position.
I would expect the amperage, two to three hundred amps maybe, when cranking the engine would far exceed the current carrying capability of conventional split charge wiring though.