It is not only in the operator's own interest to make sure that they are maintained in good condition but it is his duty to look after them.
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.