I would like to point out that a majority of those batteries, unless you start using fancy stuff like Optimas, are filled with liquid battery acid (battery acid = sulfuric acid). I have worked with these batteries for years and have seem them leak like there is no tomorrow when tilted or 'sloshed-about'. Although getting the acid on you will not melt your arm off like in the movies, it will itch like like fire and put holes in your clothes the next time you wash them. If it falls into your plants water-source, it will drastically change the PH.

So if you are going to be using some of those cheaper batteries, make sure that the caps are on tight and keep them level!