Hey everyone...first of all, let me say that I am NOT mechanically inclined. I've never worked on vehicles and I don't particularly care to. I just want them to work, lol. That being said, I'll try to give you a good idea of what my situation is; if more info is needed, I'll be happy to provide to the best of my ability.
This summer, I bought a '98 Jeep Grand Cherokee off of Craigslist. My boyfriend (who has far more experience with buying/working on vehicles) gave it a good look over. We test drove it, looked at the engine, tires, brakes, etc.
This summer, I let it sit for about 9 days while we were on vacation. When I tried to start it up, the battery was dead. We jumpstarted it, and it held a charge for awhile, but gave signs of dying over the next few days (slow to crank over, weak idle, then would start back up fine after it had been driven around town). So, we figured it was an old battery (it looked old), and just needed to be replaced.
The new battery worked well for several months until winter came. After our first very cold night, the battery was completely dead. Thinking it might be the starter (in retrospect, it was obviously just a dead battery, we just assumed it had to have been something else since it was new), so we changed that. Then had to jump start it. We put it on a trickle charger over night. And it worked for a few weeks. Next cold night? Weak battery, so we just hooked it up to the trickle charger.
Long story short, over this winter, I have probably charged it on the trickle charger about 10 times. It's gone completely dead to the point of needing a jump start twice. Last night, it was completely dead, we jumpstarted it, moved it to the trickle charger, charged it over night, and this morning it barely started and still had a weak idle (it was below 0deg last night).
The alternator has been checked, and it was fine (done at a shop). I don't know enough to know of any other issues, but I'm not convinced that it's just the battery. My boyfriend thinks it's just a faulty battery. I have the receipt for the battery, but I'm not sure if Walmart would accept it 5 months after I purchased it. I'm just hesitant to pay another $100+ for a battery if it's not going to fix the problem.