Sounds to me like you have done all you can ... by running more than one Equalize charge. By your own admission the battery has been abused by neglect and lack of decent charge maintenance -- plus its at least two years old. The plates are probably heavily sulfated ... there are devices that 'might' remove that but the cost will exceed a new battery. Get a new battery. .. at least a Marine type deep discharge battery instead of a car starter type like you have now -- and don't allow it to discharge below about 12.2 volts. You should be able to get four or five years out of a properly maintained battery.
