2000 Dodge Intrepid starting/charging

Hi! This is my son's car - it's been a great car for a couple of years - no problems. Then about a month ago, the battery died. Freezing in Michigan! We got a new battery, and it was fine. Then about a week ago, dead again. This time it was the starter. They put in the new starter and it only started for about another 1-2 days. We had it towed back again, of course, and now they're saying there's a draw on the battery somehow, and they can't figure it out. I'm wondering if you might have a clue. It does have a stereo system in it, but it's been there for 2 years and never a problem on the battery thus far. Is there something particularly from changing the starter that could have been hooked up wrong, or?

Any direction could help. It's just sitting there right now. UGH! I'm a single Mom with a college kid, and just can't afford to continue to tow it all over! Thanks for any advise!