Same problems with my webasto systems. I run 2 batteries crossed over, and all is connected to a trickle charger. Anyway, leisure batteries are normally deep cycle, and i spoke to an auto electrician, well the guy at my local webasto dealer and explained my issues. He says as the batteries are getting a constant charge, you are messing them up. You need to remove the batteries at least once a month, or even better once a week, stick a light on the batteries to run them flat, then mains charge them. I have started to do this, so time will tell. He says the Ambulance/Army service are constantly going through batteries due to this very reason!