A battery, such as a D battery, is a device that the generates electrical energy. Batteries are convenient portable sources of energy. Unlike other other the energy-conversion devices, batteries contain no moving parts. Batteries convert chemical energy into the electrical energy by means of a chemical reaction.
Amount of Current
A standard D-size carbon-zinc battery has an amp hour capacity of 4.5. This means that a D battery could supply current of 4.5 amps for one hour. This can also be calculated as the D battery supplying a current of 1 amp for 4.5 hours, or any other the combination with this same formula.
You should keep in mind though, that this is the only a guideline. If you are running the D battery at a maximum current of 4.5 amps, the amount of heat would cause the battery to lose part of it is a chemical reaction, causing it to be fully discharged before the one hour span. The same is true for an extremely light load as well. For example, if battery was connected to a load of just 1 milliamp, it would give current for 4,500 hours. But, more than likely, evaporation of the chemicals needed for the reaction would also cause the battery to lose charge before the 4,500-hour mark.