Andrew & Kate Lamb
Ok sounds like I should leave well alone - in our last boat the -VE poles were tied together between the house and engine batteries with one common (black) master switch and the positive poles had separate (red) master switches the combined circuits were isolated though. I am keen to monitor the battery state as the only charging appears to be from (I think) the genset or engine alternator and given that both of these need the battery to be charged to start... - there appears to be no charging from the shore power - I think I will install a separate battery monitor, to monitor the health of the engine battery. Good tip on the jump leads - I did come across these at the bottom of a locker.
Andrew & Kate