While it is possible your alternator isnt charging right or that your have something draining the battery while it is parked, I'd guess the battery is most likely the issue.

There is no need to charge the battery, the alternator does that. My car usually sits for 12-14 days at a tine and mine starts right up - on a four year old battery in temps of 35f.

You have something wrong.... my guess is its the battery but who really knows.