1995 Maxima electrical/starting problems

My 95 Maxima had 150,000 miles (just turned over 84 miles ago) and I have had barely any problems with it. Yet ever since I bought it, roughly 3 years ago, it has had trouble starting in the dead of winter.

Over the years the problem has gotten worse- at first the lights came on when I opened the door, and the engine would struggle a little, but 3 years later-- in fact, this happened tonight-- now the lights dont even come on and the battery is completely dead when it gets cold out.

I routinely have to have it jumped in order for it to start, and we have checked out the entire electrical system, done numerous battery checks/replacements, etc. All to NO avail. I am out of ideas on how to fix this problem. Replacing the battery works, but only briefly. I thought maybe replacing the alternator would help, but that hasn't happened yet, mainly because if the body shop says the alternator works fine (and they do) I dont want to replace it.

HELP! Any suggestions on what I should do, or has anyone else had this issue? Thanks