is my battery ruined?

Missed with batteries for years, as a farmer and Farm equipment dealer. It might make it ok, but i"m sure the life had been hurt. I had mine go down last fall, do to leaving heater fan on by accident. Had to install new roof and told them of the down batteries, as I had no way to charge where I was at. They promised me they would charge the batteries. I suppose they didn't. In the meantime we got freezing weather. They held a partial charge, but since we would be gone for several months I replaced with new batteries. That is your choice. Since it is winter it might make it, but my guess is it is dying. Take it to someone who can charge it all the way, then take a testing unit that can put a load on it. That will tell you how good it is. If will will hold up under a load test you will probably be ok. Be sure and charge back up after a load test.