one thing you might want to try. battery stores have saved many battery by doing this. Put a car battery charger on the battery. turn the switch to engine start for about 5 minutes or so. don't let the battery get too hot and it would be wise to put a shop towel over the vents so you don't get acid in your eyes when you work around a battery. after the time limit, put the charger back on manual or auto charge and charge over night. then test the battery to see if the charge is up over 13.2. if not then the battery is shot, get a new one
If you use this method (the famous mexbungalows HF trick), just be sure the voltage doesn't climb much above 16v while pouring the amps in manually. You are going to see some bubbling - this is normal and you might need to top off the cells with distilled water afterwards. You can probably go for an hour or two of manual charging - just keep an eye on it. And get a hydrometer - its really the only way to check battery condition properly.