The acid doesn't go away- just the water. If you add acid, you mess up the mix in the battery and it will croak. The specific gravity gets out of whack and the current doesn't flow properly. It will ruin the battery.
Oh, and on the battery/concrete deal, it just isn't so. Batteries will not go dead sitting on the ground. They are insulated by their plastic housings. Ever wonder why they can sit on a steel shelf and not go bad? Steel is a conductor as well. The adage about not putting them on the ground is an old one though- and it used to be true. When batteries were in their early stages of development, most were in wooden cases. ( Remember, "plastic" is only about 50 years old.) These old batteries would go bad sitting on the ground because the wood would leach the acid/water mix through the wood and provide a pathway for the current. They WOULD go bad over time. With the advent of plastic non-conductive cases, that problem went away. Try it sometime- charge up your battery and sit in the the corner of your garage- go back a month later and check it. It may lose some charge just as any idle battery will, but it sure won't be anywhere near dead if it was a good battery to start with.
UFM82