Digital cameras have high power requirements, and over time have become smaller, resulting in an ongoing need to develop a battery small enough to fit in the camera and yet able to power it for a reasonable length of time. Two broad types of batteries are in use for digital cameras. [edit]Off-the-shelf Main article: Commercial off-the-shelf Off-the-shelf batteries may be single-use disposable or reusable rechargeable batteries. In either case they conform to an established off-the-shelf form factor, most commonly AA, CR2, or CR-V3 batteries, with AAA batteries in a handful of cameras. The CR2 and CR-V3 batteries are lithium based, and intended for single use. They are also commonly seen in camcorders. AA batteries are the most common; however, the non-rechargeable alkaline batteries supplied with low-end cameras are capable of powering most cameras for only a very short time. They may serve satisfactorily in cameras that are only occasionally used. Consumers with more than an occasional need use AA Nickel metal hydride batteries (NiMH) instead, which provide adequate energy and are rechargeable. NIMH batteries do not provide as much energy per volume as lithium ion batteries, and they also tend to discharge when not used. For the same energy, a NiMH rechargeable battery takes up to twice the volume of a Li-on rechargeable battery, and is three to five times heavier, but only costs half as much. Rechargeable batteries are available in various ampere-hour (Ah) or milli-ampere-hour (mAh) ratings, which are approximately proportional to shots per charge. Typically mid-range consumer models and some low end cameras use off-the-shelf batteries; only a very few DSLR cameras accept them (for example, Sigma SD10, or some Pentax DSLRs via an optional adapter). However, most battery grips for DSLRs come with a separate holder to accommodate AA cells. Rechargeable RCR-V3 lithium-ion batteries are also available as an alternative to non-rechargeable CR-V3 batteries. Cameras, especially earlier ones made for AA-size batteries assumed that these would be of the non-rechargeable, preferably alkaline manganese type delivering 1.5 volts per cell. Rechargeable NiCd or NiMH cells only deliver 1.2 volts, which means that many such cameras will only operate for a short time or not at all even with new and newly charged 1.2 volt units. A portable ultra-high-endurance external power-supply for the shoulder bag to operate older 6 volt cameras can be made up of five 1.2 volt C-size cells which can be either NiCd or NiMH, with a cable and 4mm DC-plug. [edit]Proprietary The second type of battery for digital cameras is proprietary battery formats. These are built to a manufacturer's custom specifications, and can be either aftermarket replacement parts or OEM. Almost all proprietary batteries are lithium ion. While they only accept a certain number of recharges before the battery life begins degrading (typically up to 500 cycles), they provide considerable performance for their size. A result is that at the two ends of the spectrum both high end professional cameras and low end consumer models tend to use lithium ion batteries.