Recharging alkaline batteries is a way of renewing expended alkaline batteries

Alkaline battery

Alkaline batteries are a type of primary batteries dependent upon the reaction between zinc and manganese dioxide . A rechargeable alkaline battery allows reuse of specially designed cells....

 and alkaline cells.

A rechargeable alkaline battery

Rechargeable alkaline battery

Rechargeable alkaline battery is a type of alkaline battery that is rechargeable. The first generation rechargeable alkaline technology was developed by Battery Technologies Inc in Canada and licensed to Pure Energy, EnviroCell, Rayovac, and Grandcell...

 is designed to be recharged. Common types are primary cell

Primary cell

A primary cell is any kind of battery in which the electrochemical reaction is not reversible, rendering the cell non-rechargeable. A common example of a primary cell is the disposable battery. Unlike a secondary cell, the reaction cannot be reversed by running a current into the cell; the chemical...

s, and it may be dangerous to attempt to recharge them. Manufacturers of primary batteries expressly forbid recharging. Despite this advice, some alkaline batteries have successfully been recharged. Sometimes chargers can be found on the open market that claim to recharge primary alkaline batteries. The performance of a recharged primary battery can be unpredictable.

Introduction

Ordinary alkaline batteries can be charged with a current pulsed at a rate of 40 to 200 pulses per second, with an 80% duty cycle

Duty cycle

In engineering, the duty cycle of a machine or system is the time that it spends in an active state as a fraction of the total time under consideration....

. Pulsed charging appears to reduce the risk of electrolyte — usually potassium hydroxide

Potassium hydroxide

Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...

 (KOH) — leakage. The charging current is usually very low to avoid rapid production of gasses that can rupture the cell. Cells that have leaked electrolyte are a safety hazard and unsuitable for reuse.

Safety

Attempting to recharge a discharged alkaline battery can cause the production of gas within the canister. As the canister is normally sealed, very high pressures can be created within it. This can rupture the seal, resulting in leakage of the contents — for example, aqueous potassium hydroxide and identifiable in more severe cases as a hissing sound from the battery — or even an explosion. Warning signs include bulging of the ends of the battery. Recharging a battery produces heat within the battery. Sometimes the heat can be excessive, with the attendant risks of fire, explosion and/or injury.

Potassium hydroxide is corrosive and may cause injury, especially to the eyes and skin, or corrode the battery contacts in the equipment. Eye protection is always advisable when recharging any batteries.

Some materials used in batteries are damaging to the environment. In some jurisdictions it is illegal {cn|date=November 2011}} to dispose of batteries in ordinary waste streams and free collection points for used portable batteries are often available wherever batteries are on sale to the public.

How it works

As an alkaline battery is discharged, chemicals inside the battery react to create an electric current

Electric current

Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

. However, once the chemicals have reached chemical equilibrium

Chemical equilibrium

In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

, the reaction stops, and the battery is depleted. By driving a current through the battery in the reverse direction, the equilibrium can be shifted backwards towards the original reactants. Different batteries rely on different chemical reactions. Some reactions are readily reversible, some are not. The reactions used in most alkaline batteries fall into the latter category.

External links

• Afroman's guide to recharging alkaline batteries — Personal experimental data (contains strong language, however technically accurate)
• Charging the unchargeable — Improved alkaline charging circuit
• Potassium hydroxide MSDS from JTBaker