So a development this morning:

Thus far I haven't had any issues while driving the car even with the batter light on. I noticed today it went off and on a bit when depressing the clutch and shifting gears. However, a mile or so from work, my radio cut out, the spoiler light blinked and my ABS and BAS ESP lights came on then went off. I turned off the radio and AC, put down the windows and proceeded to pray for the next 10 minutes while I was stuck in traffic. Mechanically, everything seemed to run fine and the car did not sputter or die. However, the windows wouldn't go up and the ABS/BAS lights kept coming on and my spoiler is now up. I know the spoiler is a classic sign of a bad battery, but my question is this:

Are the "accessories", i.e. windows, radio, spoiler powered by the battery or the alternator while the car is running? Specifically, I'm wondering if maybe my battery was indeed bad and not charging correctly. OR is the alternator dead and thus not able to charge the batter?

Basically, I'm going to run to the auto parts store on my lunch today but I don't know if I should just buy a new battery, or if I should jump my car (assuming it won't start, though I haven't tried), try to drive it there and see if they can recharge the battery and test the alternator. Long story short, I don't want to buy a new battery if I don't have to, but if its just the battery that is the issue I would love to just get a new one and be done with it!

Need some advice. As previously mentioned, I'd rather not spend money on the wrong thing.