Hello! I think I have the same problem!!!
I have a Nissan Micra 2003 2.1V. It has only recently become a problem as I have just stopped using it everyday.
The battery is being drained over a period of about one week. Before when i was driving it during the week it was absolutely fine over weekends and things but as I am not using it so often this problem has become apparent. I have changed the battery and that had made no difference. I have also switched things off in the car such as the radio and interior light so they can't flick on somehow and there is still a problem! All it needs is a jump start to get going and it is absolutely fine! I really love car!
I have also had a auto-electrician come to look at it who couldnt find a drain from the battery (testing it with an ammeter) so it seems that something is kicking in when it is off and draining the battery!?
Do you have any idea how I could fix this? I am being quoted so much money which i can't afford! I know you are lucky enough to know someone but any more info would be very much appreciated! I know its a long shot! Thanks you!