Car battery died, was successfully jumped, then died again hours later

What is your question?

I left my car door slightly open on Friday. I noticed it on the following Sunday and checked to see if the car was dead. It was and I wasn’t surprised because there’s a light that stays on when the door is not completely closed. It was completely dead - no lights or anything came on. I jumped it the next day (today) and it started easily and I let it run idle for 20 minutes. About 4 hours later, I tried to start it and it was dead again. My lights came on, but nothing else. Is it possible that I just didn’t let the car “charge” for long enough or does it sound like my battery or alternator is messed up?