Mercuric Oxide: Mercury batteries were commonly used in many classic cameras of the 1960s and 1970s for their CdS (cadmium sulfide) metering systems. Mercuric oxide batteries provide a constant and stable 1.35 volts over most of their life. This means that the camera does not have to have voltage regulation circuitry, considerably lowering the cost of production. Unfortunately, mercury batteries were outlawed in the U.S. in the 1980s and are not readily available anymore. However, all is not lost. There are several solutions below.
Alkaline (zinc/manganese dioxide; Zn/MnO2): This is the chemistry used in your standard alkaline battery (C, D, AA, AAA, etc.). New batteries give 1.5 volts which quickly declines over the life of the battery. Alkaline batteries have high internal resistance which means they will not discharge quickly. This reduces their usefulness in high-drain devices such as camera flashes or motor drives.
Standard and Heavy-Duty (zinc/carbon and zinc-chloride): This is the chemistry used in “standard” and “heavy-duty” batteres (C, D, AA, AAA, etc.). New cells give 1.5 volts which quickly declines over the life of the cell. Zinc-Carbon batteries have less than a third of the storage capacity of “Alkaline” (ZInc-Manganese dioxide) batteries and we do not recommend their use in any situation.
Silver-Oxide: Starting in the 1970s, camera manufacturers started to move to silver-oxide “button” batteries. Silver-oxide cells provide 1.55 volts fresh out of the can, but then the voltage slowly drops over the life – not as much as alkaline batteries, but more than mercuric-oxide. This means that cameras could not depend on the voltage being stable and started to use what are called “bridge circuits” to reduce the effect of the falling voltage.
Lithium-Manganese-Dioxide (LiMnO2): Into the late 1990s, even relatively simple mechanical cameras such as the Leica M7 were power-hungry as they had sophisticated CPU units drawing power. Camera manufacturers started to push the use of lithium cells with Lithium Manganese-Dioxide (LiMn02). These cells have names that start with “CR” such as: CR2032, CR1/3N, or 2CR5. Based on light metal chemistry, lithium cells have incredible storage capacity for their size — many times that of alkaline or silver-oxide batteries. They also have much better cold weather performance as well as a shelf-life of 10+ years. The only downside is that lithium is a pollutant, so dispose of your lithium batteries at an approved recycling center as LiMnO2 cells are not rechargeable.
Lithium-Iron-Disulfide (Li-FeS2): The Li-FeS2 lithium cells are a relatively new phenomena. They produce 1.5 volts, which allows them to be used to replace zinc-manganese batteries in common sizes like AA and AAAs. These lithium cells have longer shelf-life and better high-drain capacity which makes them suitable for use in flashunits and digital cameras. In fact, although on paper Li-FeS2 doesn’t have considerably more capacity than its alkaline equivalent, one manufacturer test noted that a consumer could get up to 10x the digital camera shots using their lithium replacement AA cells compared to using standard alkaline. The only downside? Li-FeS2 cells are twice to three times the price of standard alkalines.
Rechargeables: Nickel-cadmium (NiCad) batteries are rapidly being eclipsed by newer Nickel-Metal-Hydride (NiMH) rechargeables. In addition, NiMH doesn’t have the same toxic chemical (cadmium) found in NiCads. In the common AA size, NiMH batteries can store up to 2400 mAH. Unlike alkalines, NiMH have low internal resistance which makes them ideal for the fast refresh cycles of camera flashes (warning: not all flash units are compatible with NiCad/NiMH batteries). For digital cameras, NiMH itself is rapidly being replaced with Lithium-Polymer, Lithium-Ion, and other lithium chemistries.