My 2004 Ford Freestar frequently has to be jumped to start. Once jumped, if I drive it for more than 15 min or so, it'll stay charged enough that I can drive it again within the next day or so. If I leave it in the garage for two days or more, it won't start and needs to be jumped again.
I believed this was the alternator's fault, so I had it replaced. It didn't fix the problem. I had the battery checked at the auto parts store and they said it was good. They suggested something about the ground or that I might have something plugged into the cigarette lighter (I don't). I followed the ground wire at their suggestion and didn't see anything suspicious. The connectors are all pretty clean.
UPDATE: I checked the voltage with my multimeter. With the car off, the battery registered about 12v, with the car running, it registered just over 14v. So my understanding now is that the battery and the alternator are probably not the problem?
The battery is one year old.