Mines a 2006 with 6 CD changer in the dash and the satnav under the passenger seat.

Radio and satnav now playing up every morning and evening when I finish work.
BUT if I switch on the program button for the front and rear screens it stops and works fine. Any thoughts??

No thoughts but I have had a problem with my Radio/Cd volumne switching off for no apparant reason on my 2006 model with 6cd stacker. Still haven,t solved that one.
Just a note on your use of a smart charger and the voltage drop.
All the smart chargers I have come across actually discharge the battery before recharging over a 12-24hr cycle. 2006 4.2 S/C with Tow Pack, Side Steps, DRL's, 19" & 20" wheels, additional 110 ltr Fuel Tank Roof Rack and performance mods.

1952 Rover 75 (Cyclops) First Car !!! Fond memories -was restored-good for 93mph.