Changed the relay for the auxillary socket from a normally open to a normally closed, with a bit of wiring, so it's live with the ignition off, not on.
I drive to work very early on Monday morning, 15 mins, out all week in a truck, then drive back home Friday evining.The car can then sit all weekend, so sometimes suffer from a flat battery at this time of year.
A £10 Maplins 1.5 amp solar charger plugged into the aux socket should keep the battery topped up. I have a spare battery in the boot connected to one of these solar chargers and it's always fully charged for jump starting