Alternator? or battery?, im not sure which one Options

[Goonter]

ok im not sure which one is busted but i'm thinking the alternator. last night came from a new year's party and i started my car. all of a sudden the battery light came on, which was weird cause the car was already running and it should've been charging while the car was on. so i went to my gf's house and slept over. this morning i started my car , battery light was on yet again. then i went inside to let my car warm up.. i went back out after 10 minutes and my car was dead. i found it weir again cause the car was running and the battery shouldve been charging. i tried to start the car again but no cranking or anything. but when i get a boost from a battery pack the car starts up no problem. so do you guys think it's the alternator? thanks in advance for the input

[96stgreendemon]

as low as 20 and as high as 80, of course this is ebay so not sure of autozone, just click herehere