This is a weird one. In the winter months (UK) I use a weather cover on my E46(2006), more to protect the soft top over the winter months than anything else. The cover isnt fully waterproof.
Recently I have noticed that when I take the cover off, the car refuses to even crank over. Clock is on, radio ok, no discharge warning, nothing that would lead me to suspect a battery problem.
When I then leave the car for 1 hour it cranks over no problem. Almost as if humidity or moisture somewhere is the cause but once the cover is off this clears.
Other info, there is no damp or water ingress in the boot/trunk areas, all battery terminals are clean and tight. Ive checked key fob etc - tried two different keys etc., all good.
Can anyone shed any light on this?