Alkaline battery

An Alkaline battery is a type of power cell dependent upon the reaction between zinc and manganese dioxide (Zn/MnO2). Compared with traditional zinc-carbon batteries, while both produce approximately 1.523 volts per cell, alkaline batteries have a higher energy density and longer shelf-life. Compared with silver-oxide batteries, which alkalines commonly compete against in button cells, they have lower energy density and shorter lifetimes.

Chemistry
In an alkaline battery, the anode (negative contact) is made of zinc powder and the cathode of manganese dioxide. So far, they are comparable to zinc-carbon batteries, but the difference is that alkaline batteries use potassium hydroxide (KOH) as an electrolyte rather than ammonium chloride or zinc chloride. The half-reactions are:
 * $$\mathrm{Zn} + 2 \mathrm{OH^-} \rightarrow \mathrm{ZnO} + \mathrm{H_2O} + 2 e^-$$

and
 * $$2 \mathrm{MnO_2} + \mathrm{H_2O} + 2 e^- \rightarrow \mathrm{Mn_2O_3} + 2\mathrm{OH^-} .$$

Capacity
Unlike NiMH rechargeable batteries, alkaline batteries are normally not sold with a nominal capacity. The reason for this is that the capacity of an alkaline battery is strongly dependent on the load. An AA-sized alkaline battery might have a capacity of 3000 mAh at low powers, but at a load of 1000 mA, which is common for digital cameras, the capacity could be as little as 700 mAh.

Leaks
Over time, alkaline batteries are prone to leaking potassium hydroxide, a caustic agent that can cause respiratory, eye and skin irritation. This can be avoided by not mixing different battery types in the same device, replacing all of the batteries at the same time, and removing batteries from devices for storage.