The voltage supplied by a battery is determined by the chemicals inside the cell. Voltage is highest when it is new or immediately after being charged. It will decrease as it is used. When it is dnearly ischarged, the voltage will fall rapidly. The nominal voltage for zinc-carbon and alkaline cells is 1.5 volts. For NiCad and NiMH, the voltage is 1.2 volts. For Li-ion cells, it is 3.6 volts. Battery cells are usually connected in series to create higher-voltage batteries to drive the electronics in the camera.
The storage capacity of a digital camera battery is a measure of how long a camera will operate before the battery needs to be replaced or recharged. The weight of the battery is included as a factor in this measurement. The larger the size the more capacity it has. For example, a C-size battery will have a much larger capacity than an AA-size battery. If cells of the same physical size are compared, the Li-ion cells will have the most storage capacity, followed by the NiMH cells (which have about 60 percent of the capacity of Li-ion), then the NiCad (with about 40 percent of the capacity of the Li-ion cells).
Any battery will self discharge as it ages. The NiCad and NiMH batteries lose their charge relatively quickly. The NiCad battery will self discharge approximately 10 percent of its charge during the first 24 hours and an additional 10 percent during each subsequent month. This rate will increase as the temperature rises such as when it is a warm car. The NiMH battery will dissipate its charge even faster, at about a 50 percent higher rate. The Li-ion battery will lose its charge at a rate of about 6 percent per month.
The capacity of a battery is a function of its size, the voltage output and the amount of current it can deliver before it is discharged. The lowest capacity cells are the zinc-carbon, alkaline and rechargeable alkaline. The NiCad rechargeable cells have a reasonable storage capacity. The NiMH rechargeable cells can store about 50 percent more than an equivalent size NiCad. An equivalent volume Li-ion has about 175 percent of the NiMH cell capacity. All of the types mentioned exhibit a relatively flat voltage output until they are nearly discharged at which point the voltage starts dropping.
Instead of purchasing disposablebatteries, many camera owners use rechargeable batteries. These batteries can be used over and over again, and they often last a lot longer than regular disposable batteries.