I hope you can reclaim it.
Here is a do it yourself desulfator project if a conventional charger is not enough.
http://www.alton-moore.net/graphics/desulfator.pdfThe author says it can take a month to break up the large sulfate crystals
Sample quote
Usage
It should be emphasized that pulsing energy to and from the battery happens at less than 100 percent efficiency. This circuit draws about 40 mA from the battery while in operation (less than 1 amp-hour per day), so some additional charging source is needed. For reconditioning a sulfated battery, I simply clip the circuit across the battery terminals in parallel with a 30 watt solar panel.
In my initial testing, it took a month to partially reclaim a pair of golf cart batteries that had been allowed to sit, discharged, for almost a year. They had such a high internal resistance that a very small current would take the terminal voltage over 16 volts.
For use in a functioning power system, you can clip the circuit across the main battery terminals, using as short a lead length as possible. When external equipment, such as an inverter, is connected across a battery bank, then additional low impedance paths are formed. The desulfator’s current pulses will happily flow down these paths as well, and it serves no purpose for the pulses to flow into the inverter.
End quote
