The other day i was driving home and the battery sign on the dashboard came on. i kept driving and my car stalled. My lights went dim and my spoiler came up and wouldnt go down. I got it towed home and the next day i took the battery to autozone to test it and they said it was no good. I had to buy a new one for $140. When i put the battery in it started with no problem but i noticed that my lights still seemed dim. Then i thought that maybe it was just a mind thing. The next day after that i drove to the gas station and after i pumped my gas i tried to start it and it wouldnt.My spoiler came out again and wouldnt go down and my windows would go up or down. I waited about 30mins and it started. I made it home which was just around the corner and the car seemed to be struggling to get there. I havnt tried anything since that because i aint wanna drain the battery. Any suggestions on what i should do or what the problem may be? If it is the alternator how much would that cost to replace?

Thanks in advance