restoring gel batteries

[BANE]

Hello all,
I have two powersonic 12v 33amp hr sealed gel wheel chair batteries that wont hold a charge and give 22v in series.  I was going to chuck them but i thought i'd give restoring them a try since they look fairly new.  I popped open the caps and they where super dry; it took about 100ml of water per cell to fill them up.  After a recharge they now give around 25v but under heavy current draw the batteries release a good amount of air as well as get hot.  Im thinking then water mixes with the acid oxygen is produced in an exothermic reaction and hopefully will stop after all the reactions take place.

the batteries preform about %50 better now but still only about %75 compared to brand new ones.  My questions is: i only added water to each cell, should i have added some sulfuric acid as well?

any input on if this is a good idea or a bad one or any comments are appreciated  

thnx