battery drain

....I've noted that if left, my Z's battery drains down after 2/3 days. Haven't really spent time to try and find the fault as I've got a spare battery on trickle charge. Out for a drive to football on Thursday night, lovely drive. Really enjoy driving the Z when I had a light bulb...

Just went to go out in the Z after not using for about 3 weeks and battery totally flat. This also happened a few weeks ago but thought that it was due to lack of use and testing/checkin/unlocking and locking doors but no. Casually speaking to a Z owner from Porlock in a Minehead carpark weeks...