Alkaline battery

Alkaline batteries are a type of power cell dependent upon the reaction between zinc and manganese (IV) oxide (Zn/MnO2).

Compared with original zinc-carbon batteries, while both produce approximately 1.5 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.

The alkaline battery gets its name because it has an alkaline electrolyte of potassium hydroxide, as opposed to the acidic electrolyte of the zinc-carbon batteries which are offered in the same nominal voltages and physical size.

Chemistry
In an alkaline battery, the anode (negative terminal) is made of zinc powder (allows more surface area for increased rate of reaction therefore increased electron flow) and the cathode (positive terminal) is composed of manganese (IV) oxide. When describing standard "AAA battery", "AA battery", "C", "sub-C" and "D" type cells, the anode is the flat end while the cathode is the end with the raised button.

Alkaline batteries 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, have the ability to deliver more current (although not necessarily more amp-hours), and have a longer shelf-life than zinc-carbon and zinc chloride batteries.

The half-reactions are:
 * $$\mathrm{Zn (s)} + 2 \mathrm{OH^- (aq)} \rightarrow \mathrm{ZnO(s)} + H_2O(l) + 2 e^-$$

and
 * $$2 \mathrm{MnO_2 (s)} + \mathrm{H_2O (l)} + 2 e^- \rightarrow \mathrm{Mn_2O_3 (s)} + 2\mathrm{OH^- (aq)} .$$

Capacity
Unlike NiMH rechargeable batteries, alkaline batteries are normally not sold with a nominal capacity. Alkalines have a high internal resistance, and a high thermal coefficient of resistivity — the faster an alkaline battery is drained, the higher percentage of the load it dissipates as heat. Therefore, the capacity of an alkaline battery is strongly dependent on the load, even at moderate loads. An AA-sized alkaline battery might have an effective capacity of 3000 mAh at low power, but at a load of 1000 mA, which is common for digital cameras, the capacity could be as little as 700 mAh.

Current
The amount of current an alkaline battery can deliver is roughly proportional to its physical size. This is a result of decreasing internal resistance as the internal surface area of the cell increases. A general rule of thumb is that an AA alkaline battery can deliver 1000mA without any significant heating. Larger cells, such as C and D cells, can deliver more current. Applications requiring high currents of several amps, such as high powered flashlights and boom-boxes, will require D sized cells to handle the increased load. Volume for volume, alkaline batteries have inferior current handling capacity when compared to other chemistries like NiCd and NiMH. However, alkaline batteries cost significantly less.

Recharging of alkaline batteries
Recharging of alkaline batteries is uncommon, but possible. When recharging an alkaline cell one must take into account 3 factors: Charging current, termination voltage and cell temperature. An alkaline cell can be safely charged with a constant current source of 100mA or more. The termination voltage should not exceed 1.5 Volts per cell. An ideal charging circuit will supervise cell temperature while charging.

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 attempting to recharge alkaline cells, not mixing different battery types in the same device, replacing all of the batteries at the same time, storing in a dry place, and removing batteries from devices for storage.

Disposal
Unlike other types of batteries, Alkaline batteries can be disposed of in the regular trash in some locations. The state of California, however, has made it illegal to throw alkaline batteries in the trash. In Europe the battery disposal is controlled by the WEEE regulations, and as such alkaline batteries must not be thrown in with domestic waste. They should be disposed through local recycling stations / waste dumps. In the EU also most stores which sell batteries (i.e. supermarkets) can be used to dispose old batteries because they are required by law to recycle old batteries.