A 12-volt (12V) battery is a portable device capable of storing up to 12 volts of electricity. Most 12V batteries, such as those used in cars, are capable of being recharged. To understand what a 12V battery is, you must understand the basics of voltage.
A good way to visualize voltage is by using water as an example. Imagine two tanks filled with water, one large and one small, each with a small hole in the bottom. The larger tank leaks water at a higher pressure than the smaller tank, just as a higher voltage battery provides electricity at a higher rate.
A battery is basically a tank capable of holding electrons. Higher voltage batteries provide more pressure behind the electrons allowing a higher volume of electrons to pass a given point at any given time. Eventually, just like the water tank in the previous example, the battery runs out of pressure and requires recharging.
Batteries require a power source with a higher voltage to fully recharge. Generally speaking, car batteries are 12 volts. The battery is recharged by the alternator, which will have a slightly higher voltage of 12.6 volts to 14.5 volts. A running engine is directly connected to the alternator, providing a stream of electricity for the purpose of recharging the battery.
