Once both sides are coated with lead sulfate and the battery is discharged, we will need to recharge it by applying a DC current, reversing the action and converting the lead sulfate on the positive terminal back to lead peroxide and the negative back to lead. We have made one 2v cell, if we connect 6 of them in series, we can make a 12 volt battery. Now, the chemical reaction takes place on the surface of the lead, so we need lots of lead surface area to start our engines. The most popular design is a grid plate design that also supports the lead peroxide. These grids, or plates, are packed as closely as possible and then kept apart by porous fiberglass separators.
Some batteries feature a porous glass mat that encapsulates the plates.
If we are not concerned with high currents, then this is really not an ideal design. Each time a battery is cycled a small amount of lead sulfate flakes off the plates and falls to the bottom of the case. The deeper the discharge, the greater the flaking. Lead sulfate can conduct electricity, so when enough accumulates at the bottom, It shorts out the plates. So we want batteries that can survive deep discharge and recharge cycles.