Recharging alkaline batteries
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Recharging alkaline batteries is a way of renewing expended alkaline batteries and alkaline cells.[1]
A rechargeable alkaline battery is designed to be recharged. Common types are primary cells, 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. [citation needed] 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. Pulsed charging appears to reduce the risk of electrolyte — usually potassium hydroxide (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 [citation needed] 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. However, once the chemicals have reached chemical equilibrium, 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.
Note that non-rechargeable alkaline batteries that have been recharged will often have reduced voltage and current capacity, and may leak over time. For this reason, it is not recommended to use recharged primary cells in sensitive equipment or equipment with printed circuitry.
See also
References
- ^ A "battery" is an array of cells connected in series or parallel arrangements.
External links
- Afroman's guide to recharging alkaline batteries — Personal experimental data (contains strong language, and encourages theft, however technically accurate)
- Charging the unchargeable — Improved alkaline charging circuit
- Potassium hydroxide MSDS from JTBaker
- Patent describing alkaline battery charger