It could be either residual drain, or a battery on its way out - the only way to be sure is the check the battery drain.
I had a problem with discharge and explained how I tracked my problem down in the forum -
https://the75andztclub.co.uk/forum/s...d.php?t=167111
Certainly, a good battery, fully charged, with a normal level of discharge, should be able to be left parked for at least 6 weeks.