charging 2 volt forklift battery cells or 12 volt batteries in parallel

I recently bought a Clark SP 30 walk behind stacker. The machine looks like it has been used very little if at all. It came from a facility operated by Bayer. The lift has a 12 volt battery pack The battery pack still had the sticker on one of the cells stating that the battery should be given an equalizing charge upon first being charged. The battery is nearly completely discharged. From end terminal to end terminal the voltage is under 5 volts. The water in the battery is clear and was nearly up to the top of the plates - it took very little water to fill the battery. When I hook up the batter to a 12 volt charger the charger will not turn on. I believe that the battery is so discharged that the charger does not recognize that a battery is connected. I have read that one way to proceed would be to charge the individual cells - the battery has 6 2 volt cells. I can't find a charger to do that. Can anyone recommend such a charger? Additionally - Could I connect this batter in parallel with another 12 volt forklift battery that will take a charge and charge both batteries at one time? Any practical suggestions would be appreciated.

I had a "dead' 12 volt car battery that would not take a charge. I hooked up a solar panel that had no controller. It simply applied 12volts at every low amps all day long. After a few days the battery had enough back emf to take a regular charge. Many people have recommended a simple solar charger setup as a trickle charger so seldom used batteries do not go flat. Of course the panel has to get enough light do make some voltage. Inside the shop near a window or even overhead lights may be enough.

At 5 volts I'm betting that battery is DEAD. Have you checked the voltage of each cell? Put it on a plain transformer type 12v battery charger for a day or 2 and see what happens. The "smart" chargers will not even attempt to charge a battery below a certain threshold.