has anyone ever tried buying acid & topping a battery off? I have a battery not completely charging & i ordered a gallon hoping not to have to buy a new battery.

14 minutes ago, Ghostshad said:

has anyone ever tried buying acid & topping a battery off? 

No.  But, once I did spend a couple hours watching an Old Style can come to life.

Highly recommend using gloves.

Common problem with wet cell deep cycle batteries, they require maintenance!

The water is simply distilled nothing special. 
If the top of the plates are dry and exposed the battery is toast.

Flow-Rite Controls has a good watering system.
Simple filler rubber bulb made for this purpose  works if you access the fill caps.

Next battery should a AGM with zero maintenance.

Tom

You never add electrolyte to a battery once it has been initially charged.  The water is what evaporates not the acid so when you add more acid it increases what's supposed to be the proper amount and eats the plates more.  Actually, causing more harm.   

About 85% of deep cycle battery failures are from sulfation, not loss of acid.  Sulfation is caused by the battery being left sitting below approximately an 80% charge level for more than 12 hours.  

About the only way to reclaim one is to put it in an ultrasonic bath of caustic soda or something similar, (that's what companies do the "reclaim/recycle a battery" to remove the sulfation and then recharge it with electrolyte, but that's not something most individuals should be trying.  Since I'm not most individuals I have done a few but it has never proved to really be worth the danger and effort of doing it.  At the most, I've gotten maybe another years or so out of one.   After they sit too long, the plates start to flake apart also.  

Another thing is there are different levels of concentration, based on the design of the battery.  Each gives a different specific gravity.   Cranking batteries usually run about 1.26, deep cycle batteries usually run 1.28 to 1.3.  

By the way, don't think those maintainers that claim the get rid of sulfation really do.  The get rid of the early powdery stage but not that heavy crusted that you can see if you look down in a battery with service caps the see those light grey looking plates.  Those are junk.