1994 Nissan Sentra Battery keeps dieing

My car started to have problems monday morning when running into town to run errand (my dad behind me) I asked him to follow me to the bank because my car started up fine but it was raining so I went to turn on my wipers and lights. My lights were dim and wipers really really REALLY slow. My radio went out after just a few minutes after driving. At first I thought it was just the fuse needing to be replaced and I checked it and it wasnt. My check engine light came on well I called my dad and told him he said it sounded like the battery until I told him my car wasnt getting up to speed (i have a stick) the RPMs werent getting high enough to shift I had no tork and the engine temp. Wasnt getting high enough, he then changed him mind and said sounds like the alternator and said when we got to the bank to not turn off the engine (a given) well as soon as I pulled into the parking lot and popped it into nuetral to coast in the engine quit. I had someone take me to get a new alternator to change it out after we did they jump started it to let it charge after they shut it off to check if it would start again it didnt and then the battery light was on. The battery was dead. They took it to walmart and had them charge it to see if would hold a charge they said it was but ass soon as we put it in my car the charge was killed my battery was once again dead. We checked the alternator to make sure it wasnt faulty and it was fine. When I went to work tonight (wednesday) my friend told me she was having the same problem with her car a couple months back. Which is still in the shop. And her machanic finally figured out something else in the engine was draining the battery but he never told her what it was. Can you possibly save me from expensive no need repair bills? Plus im about to move in a week.I dont need to spend extra money!

thanks