Aight well first it sounds like it may be your battery. I would go take it to like autozone and have them test it. If it shows out to be ok then start your car, get a multimeter (if you have one) and measure the volts accross the battery post. If its above/about 14volts your alternator should be ok, unless its at like greater then 16volts.Turn car off and check the alternator belt and make sure u cant pull it off with ur hand, just make sure it seems pretty tight. And if you get another battery get the one that has the max RC/AH time and most CCA you can get to fit in your car. Most RC/AH time is probably most important since u are carputing.