The volt (symbol: V) is the derived unit of electromotive force, commonly called "voltage". It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, possibly the first chemical battery.
The ampere (symbol: A) is the basic unit of electrical current strength.
An ampere-hour or amp-hour (symbol Ah , A•h, A h) is a unit of electric charge, with sub-units milliampere-hour (mAh) and milliampere second (mAs). One ampere-hour is equal to 3,600 coulombs (ampere-seconds), the electric charge transferred by a steady current of one ampere for one hour. The ampere-hour is frequently used in measurements the quantity of electricity (capacity) of a battery or cell is usually expressed in ampere hours.
Cell The smallest unit of a battery, consisting of a positive and a negative electrode, a separator and the electrolyte. Cell stores electrical energy and forms the fundamental cornerstone of a battery if it is placed into a case and equipped with electrical connectors.
Changing a battery
In modern automobiles, the grounding is provided by connecting the body of the car to the negative electrode of the battery, a system called 'negative ground'. In the past some cars had 'positive ground'. Such vehicles were found to suffer worse body corrosion and, sometimes, blocked radiators due to deposition of metal sludge.
Plates are composed mainly of lead Pb. A grid, made of lead and lead oxide alloyed with antimony and calcium to improve the grid's strength, construct the plate.