Batteries store electrical energy in the form of chemical energy. When electricity is drawn from a battery, a chemical reaction occurs inside the battery. The battery will continue to produce electricity until all the chemicals have been used. On any vessel there will be two types of batteries, primary and secondary. They will have an expiration date and at that date, or if used, they must be replaced with new batteries.
Secondary batteries are rechargeable.
After use, or after prolonged storage, these batteries can be recharged to restore their capacity. Charging reverses the chemical process inside the battery so the battery can once again supply electricity. Secondary batteries are found in handheld VHFs, stand-by emergency batteries and, particularly on smaller vessels or yachts, secondary batteries will power the main radio systems. Most batteries are made from a series of individual cells. The nominal voltage of a cell or battery is its average operating voltage.