JamieDonaldson
...automotive service is lead acid which has a liquid electrolyte. Some are claimed to be low or no maintenance, but do require venting to avoid gas buildup that can be explosive. They do actually require some maintenance of fluid levels, but the cell covers are not always obvious. I use Optima gel cell types in my older cars, and this design doesn't have a liquid component and can be installed in other than vertical positions without venting or potentially corrosive acid leakage.