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Different battery voltages are achieved by stacking a number of cells in series. The individual cell voltage is a function of the chemistry, i.e, the interaction between lead and sulfuric acid when a current is passed through it (i.e, charged) results in an accumulation of ions with a potential of a little over 2 volts. In a standard flashlight cell, the potential difference resulting from the chemical reaction is about 1.5 volts, and in a NiCad battery its about 1.2 volts. On a lead acid battery, each cell is in its own compartment, and can be thought of as a separate battery. In a six volt battery, there are three cells packaged in a single box. In a 12 volt battery, there are six. In another example, I can put two six volt batteries in series and have 12 volts - in this case, there are still six cells but they"re divided between two separate cases. The available current is mostly a function of how fast the chemical reaction inside the battery can take place. In the case of lead-acid batteries, this is determined by the surface are of the plates in the individual cells. More plates, or bigger plates, result in more surface area and therefore more available current. Hope this helps. Keith
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