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Rechargeable alkaline batteries are available in all of the common 1.5-volt sizes, from AAA to D, in addition to nine-volt versions. Different companies manufacture a few types of rechargeable alkaline batteries, but they all use the same basic technology. These batteries are sometimes referred to as rechargeable alkaline manganese (RAM) batteries because of their specific chemical composition, which differs from traditional alkaline batteries. Traditional alkaline batteries also can be recharged with the proper equipment, although that can be dangerous under certain circumstances. Unlike rechargeable alkaline manganese batteries, traditional alkaline batteries might leak or even explode when current is applied.
Unlike other types of rechargeable batters, rechargeable alkaline batteries typically are available in all of the common sizes. Other types of batteries, such as nickel-metal hydride (NiMH) and nickel-cadmium (NiCd) typically are available only in the smallest AAA and AA sizes. Adapters can then be used to allow AA batteries to be inserted into C- or D-sized receptacles. The reason this works is that each of these battery sizes has the same voltage, and the bigger cells simply possess larger capacities than the smaller ones. Rechargeable alkaline batteries typically are available in nine-volt versions in addition to the larger C and D sizes, so they can offer more capacity.
Voltage levels and discharge rates are the other main differences between rechargeable alkaline batteries and other rechargeable batteries. Alkaline batteries offer 1.5 volts of direct current (DC) electricity, and NiMH and NiCd rechargeable batteries have only 1.2 volts. Most devices operate on this lower voltage with no issues, but that is not always the case. NiMH and NiCd batteries also tend to discharge when they are not in use — something for which alkaline batteries are not known. Rechargeable alkaline batteries have the same voltage and lack of self-discharge as traditional non-rechargeable alkaline batteries.
The way that regular alkaline batteries differ from rechargeables is in the chemical makeup of the cells, which includes the addition of manganese. That makes it safe to charge RAM batteries as many as 100 times, although specialized charging technology also can make it possible to charge regular alkaline batteries. This procedure can involve some danger because an improperly charged traditional alkaline battery might leak acid or even explode. The charging procedure also is different, because the batteries must be charged before they are completely dead to reduce the chance of leakage and increase the life expectancy. It is possible to charge a regular alkaline battery even without specialized charging equipment, though that can increase the risk of explosion.