Loss of battery charge due to the alarm system, vehicle clock, on board computer etc is normal over a period of time. Batteries also have an internal amount of self discharge and this gets worse with age.
Both the vehicle and the leisure batteries have their negative pole connected to the vehicle chassis. Without this the vehicle alternator could not charge both, the leisure battery of course via the split charging relay.
My simple method is to fit a pair of blade type fuse holders in a position that can be see every time the vehicle is entered via the driver’s door, in the foot well. One fuse holder has no wires attached, its is purely a park position for the fuse. The other fuse holder is connected one side to the positive terminal of the starter and the other side to the positive terminal of the leisure battery. This holder is clearly marked with white paint.
When the vehicle is laid up during the winter fit the 10 amp fuse in the wired fuse holder. This enables either the solar panel (if you have one) or the on-board stabilised charger unit to top up both batteries. During the summer and all other times the fuse is moved to the un-wired “park” position.
Should one forget to move the fuse to the “park” position and start the engine, the fuse will blow. So carry a few spares!
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