I've left it for 3 weeks in the past and had no problems when I came back.....we've been on a few holidays of 3 week duration and never had problems before, so I can only assume this time was due to it not being used very much beforehand, so perhaps the battery was low to start with - whereas before it was my daily driver.
The thing with the battery chargers - my car is on the drive in all weathers, just seems alien to me to have it plugged into the mains, although I appreciate people do so with no problems.
