Battery, Alternator, or something else????
 

So I have had a 2004 F150 lariat with the 5.4 Triton for the past 6 months. Up until now everything has been running great. I am currently living on a college campus without a lot of places/tools to help me diagnose what is actually wrong with my truck. Last week I noticed that my battery gauge was beginning to fall....not drastically, but it was noticeable. Shortly after, my dash read "Check charging system". The next day I drove my truck to class and the battery gauge was fine, however, when i got back to my truck from class it was dead. I got a jump start from one of my buddies. Ever since then my truck will not hold a charge for more than 5 minutes. It will also die instantly if I turn my lights on. I haven't had time to take my battery or alternator in to have them checked out yet. So until I can do so, any ideas why this is happening would greatly be appreciated!!! Thanks guys!

Your alternator has failed... suggest a motorcraft re-man due to our trucks being real picky about the voltage regulator that is some re-mans.

Thanks guys! Finally took my alternator in today to get tested. Turns out the alternator was failing. Any ideas why? I understand what the alternator does and everything, I'm just not sure about what actually causes an alternator to go bad. Any way I can prevent this in the future?

They wear out. The brushes inside are wear parts and eventually wear down to nubs, also wearing a groove in the commutator. The electronics fatigue from vibration and heat cycles.

The best way to avoid a failure would be to replace the alternator on a regular basis with a high-quality part. I don't know why most of us don't do that. Hard to tell when they'll wear out because dust from outside can get in to the wear areas and make it worse.

techrep is right, get a high quality part for replacement. Probably won't go wrong with Motorcraft. Parts store remanufactured alternators are notorious for failing rapidly, sometimes as soon as they're installed.. Don't go cheap.