Alkaline batteries get their name from the fact that their electrolyte is an alkaline potassium-hydroxide. They deliver relatively high energy density, and shelf-lives when compared to zinc-carbon and zinc-chloride batteries. Yet they are able to provide the same voltage when new. In today’s post we consider factors affecting alkaline battery chemistry and capacity.
Chemistry Delivering Alkaline Battery Performance
Alkaline batteries have negative zinc electrodes, and positive manganese-dioxide electrodes. Some of these materials are recycled during the electrochemical reaction. However, the potassium-hydroxide alkaline-electrolyte remains constant throughout.
The capacity, or total amount of energy generated is greater than zinc-chloride alternatives, because the manganese-dioxide is purer and denser. In fact, an alkaline battery can have three-to-five times more capacity than an acidic one.
Factors Governing Actual Battery Performance
However from a user perspective, capacity very much depends on the size of the load. In reality, it could range from 3000 mille-ampere hours (mAh) all the way down to 700. The voltage also declines steadily during use. This means that the actual capacity depends on the cut-off voltage of the application concerned.
The nominal voltage of a fresh alkaline cell should be at least 1.5 volts, although the actual zero-load could be as high as 1.65. The density of the manganese-dioxide, and zinc-oxide are determining factors in this regard. An individual cell is effectively flat when the voltage drops to 1.0 volt.
The actual current flowing through the circuit is proportional to battery size. For this reason, device manufacturers specify whether an AA, C, or D size cell is appropriate. Alkaline battery chemistry is not rechargeable at the time of writing. Much work needs to be done to encourage users to recycle their alkaline batteries at appropriate collection points.
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