I left my car in a parking lot for 5 days, and when I came back it had no power at all. I got it jumped and it worked just fine. After sitting overnight in front of my apartment, the next day it was dead again. Only this time, jumping it didn't work. I even tried switching the battery with my friend's.

Basically, it just didn't seem to get enough power. It sounded and felt just like a dead battery, only that didn't make sense in the situation. Do you guys have any idea what it could be?

Both the battery and alternator have been replaced within the past year. All of the fuses next to the battery are fine.

 

Have you checked the big 120 amp fuse in the fuse box next to the battery?

 

Yes, all of those fuses are fine.

 

Possibly the starter solenoid or fuel pump, it depends on symptoms. I would look into your starter first cause from what you posted it sounds like the solenoid is shot or the starter motor.

 

on the starter. I would remove and have it tested.

 

Just had a similar problem with mine last winter. Problem = starter.

 

That was my car last year. Cranked slow if it cranked at all. I had the starter "tested" at autozone and was told there was nothing wrong with it. Finally swapped starters with my other car and then car 1 started and car 2 wouldn't. Turns out the lube for the planteary gearset inside the starter had dried up and was binding the gears. But autozone said there was nothing wrong with the starter. Went to O'Reilly's and got another starter.

 

Turn the key, if you hear a click the solenoid is fine and the starter motor is bad.
If you hear no click there's no juice getting to the solenoid.

 

Tap the starter to see if might start or check the battery.

 

Take it apart and see if the brushes are worn down. Replacement brushes are only $30 (compared to >$100 for a new starter) on rock auto. I replaced the brushed two weeks ago and it has started everytime since the replacement.