Use distilled water

you do know that vinegar is an acid? Use water

You can buy car battery acid. Believe it is sulfuric, whatever, don't splash it. To add water, always use DISTILLED water to prevent corrosion of the battery cells due to minerals in the water.

you can use distilled water but you can also go to your local parts store and get motorcycle battery acid it's like 10 for a pint and that works alot better:)

Battery's of today are maintenance free. Better leave it that way or you "will" need a new battery. The acid used in Vinegar (acetic acid) is not the same type used in a battery (sulfuric acid). Besides, you will probably drop something inside of the battery cells if you take off the cap and add some distilled water. If your batter is over 5 years old, it's better to replace it before it dies at the worst possible moment.

Dumb idea, don't do it. Use any kind of clean de-mineralized water. Distilled water is good, but not absolutely necessary. Any battery labeled as maintainence free should not be touched. Also, even when just adding water, protect your eyes.

Never try and mix two types of acids. Granted Vinigar and Sulfuric are similar on a pH scale, so are water and Nitric. You may cause an adverse reaction. it you must use anything to travel to the local *Mart to get a new one.. use water... Do NOT assume it will last long. Water will allow the electrodes to remain submerged so that both your posts are in contact with the solution (acid) this is what gives you are charge. It is a Bi-metal reaction in the sulfuric acid. the electron's flow between the cells, each cell typically has enough electrons to generate 2 volts. The specific gravity (acid strength) of the solution generate amperage (needed to run things, like a starter, radio, etc). Water will lower the specific gravity signifigantly. So if you must, add water up to just below the top of the fill ports (1 per cell) about 1/2 inch down from the top. Drop in a half an old style 100% asprin to activate the solution and clean the cell membrane.... start your rig, drive to wally world and buy a new battery. Chances are, the electron flow generated from just your alternator is enough to cause the water to steam, you'll possibly hear the battery bubbling.