Range Rover 2002 TD6 battery drain. Printed circuit anomaly, strange symtoms.

Maybe this will help some one and maybe someone can give me advice. Range Rover Td6 2002. I have owned the car for over 4 years and it has had no major mechanical problems, my only gripe is an electrical gremlin. The car is always parked outside and had done 10,000 miles a year in my ownership. The problem is when the battery level drops below an 'acceptable' level for the computer, then the lighting module can find a way through the printed circuits to do strange things with any lights. In the case of my vehicle it switches on the brake lights. This problem has occurred when the car has been left standing for more than a week and the battery is more than 9 months old. 1/ One way I have found to stop this happening is to disconnect the earth lead whilst the car is standing unused - however I am undecided whether or not that is good for the computers health[?] plus I have found that by doing that it can sometimes cause a suspension fault code to appear although in my case there is not actually a mechanical fault. 2/ Another way is when you have fitted a new high quality battery of at least the amp hours recommended by Land Rover to invest in a solar trickle charger, this worked very well for my car until I foolishly forgot to disconnect it before starting the car and therefore damaged the solar charger just before leaving the car for 3 weeks - on return completely flat battery. My very good, [ in fact GREAT] L.R. specialists Mann Auto of Laurencekirk have been unable to find a battery drain. Everything appears to be shutting down correctly. I suspect that the 'acceptable' battery level for the computer is quite high! Land Rover themselves gave information on this anomaly, as far as I know there is not cost effective replacement for the faulty electrics. . . . Any advice anyone?