How old is your battery? They don't last forever (4-5 years seems about average, so if your car is an 06-08 and you are on the original battery you should start thinking about replacing it).
A short drive may help, and yes, leaving the door open probably drained it, especially if it's an older/weaker battery. You can have it load tested by a dealership or competent indy shop.
2008 E90 335i // Black Everything // photos
COBB tuned / QTP e-cutouts / Helix FMIC / cp-e DCI / AWE BOVs / Black M6 wheels + Toyo Proxes
(and yes, I am a girl)