Maintaining batteries today in the fork lifts. Running all over the place with a water container on wheels with an electric pump inside.

Many of the batteries are  6v and wired in series to increase the voltage to 24v or 36v depending on the vehicle.

Instead of the batteries having the typical snap-off covers on the cell fill points, a special connector is pressed into each cell with a hose running through them. The portable container has a special quick-connect device on the nozzle; that connects to the hose to fill the batteries quickly. Often a forklift will take a gallon or two every month.

A nice little circuit http://www.aaroncake.net/circuits/charger1.asp

Lead-acid batteries give off hydrogen gas; don't be dumb. I had one blow up in my face from a faulty charger once, one spark was all it needed. Enough force to knock you down and stun you a moment, and the acid doesn't feel too good either.