Based on the additional info you provided. I agree w/ edward t it is time to replace the batteries. The batteries die from lack of charging for 2 years. This is kinda like the myth that says if you store a battery on a concrete floor they will discharge. They only discharge from lack of use as humid air will act as medium to conduct electrical charge. This why idle batteries need periodic charging whether they are on a concrete floor, storage rack, in your boat, etc.

Certainly do not add a mircale cure to the batteries to try to "rejuvinate" them.

If you are looking to save a few bucks try contacting an Interstate battery distributor they may have batteries of your size that were "warranty returns" but were checked out and still good. I pay about $25 each (no warranty) and have had good luck with them so far.