It's possible, but more likely the battery has become "sulfated" and will need a little TLC before it's ready to go. 6 volt batteries are much more likely to recover from a long period of total discharge than 12 volts, for some reason. I reclaimed one a few years ago that had been sitting in a discharged condition in a 1950 Chevy since the mid-1980's. It worked well enough to start and run an early-50's stovebolt engine pretty frequently on a run stand in my shop for several months.
When a battery discharges, the plates inside the cells undergo a chemical change. The negative plates of a fully-charged battery are made of pure lead, the positive plates are lead dioxide, and the electrolyte is a mixture of sulfuric acid and water with a specific gravity of 1.250 to 1.265 depending on the concentration of acid the manufacturer chooses to use. As the battery discharges, both the positive and negative plates react with the acid to form lead sulfate, and the acid concentration drops. On a fully-discharged battery the liquid turns to pure water, theoretically anyway, with all the acid absorbed by the plates. No, I'm not about to put a soda straw into a battery cell and take a sip to test that theory!
Initially, that lead sulfate is a soft, spongy material, and reconverts to lead and lead dioxide easily when the battery is recharged. If the battery is left in a discharged state for a long time, the lead sulfate changes to a hard, stable crystalline form that is very hard to dissolve. Reclaiming a sulfated battery is a slow, difficult process. Put the battery on a slow charge, 5 amps or so, for several days, and check the specific gravity of the electrolyte frequently. As the sulfate dissolves, the concentration of the acid will steadily increase. When it tops out, no matter what the reading, put a slow discharge on the battery by connecting something like a headlight bulb across the posts and completely discharge it. Slow-charge again and monitor the acid strength. Discharge- - -recharge- - - -discharge- - - -recharge, etc., maybe as often as 10 times or more. Each time, a little more sulfate will dissolve. When the starter can be cranked for 15 seconds and the battery voltage stays above 4.5 volts for a 6 volt or 9.6 volts for a 12 while still cranking, the battery should be serviceable.
Jerry
