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Rechargeable Batteries

If you are anything like us you will use a lot of batteries in things like remote controllers, toys, cameras, torches, radios, cd players, clocks, etc, etc. Over a year the cost of replacing all the various batteries can add up to a significant amount of money, especially if you use the 'cheaper' ones which don't last as long.

A more cost effective approach is to use rechargeable batteries instead. A reasonable quality rechargeable battery will last for at least 500 charges and even taking into account the electricity used to charge the battery will work out far cheaper than the non rechargeable type. Manufacturers claim many more than 500 charge discharge cycles but this is under ideal conditions which few of us achieve.

A big advantage of rechargeable over standard batteries is a reduction in waste going to landfill. It is important all batteries are disposed of properly as they contain small amounts of potentially hazardous chemicals. If you don't know how the local council or waste disposal company household tip will be able to help.

The most common form of rechargeable battery for general use is the Nickel-Metal Hydride (NiMH) battery which has all but replaced the Nickel Cadmium (NiCad) types. Nickel-Metal Hydride batteries have a higher capacity than Nickel Cadmium ones and don't suffer from memory effect which can limit capacity. Popular types have one big disadvantage in the form of a high self discharge rate which means that even unused they will become flat in a few months making them unsuitable for devices used only occasionally or devices drawing extremely small currents (e. g. torches and smoke detectors). There are now available low self discharge versions of these batteries available at a slightly higher price which minimise the self discharge issue..

To get the most out of rechargeable batteries it is important that where you have a fair number they are each recharged on a first flat first charged basis. A simple way to achieve this is to make a small wooden sloping tray to hold discharged batteries and always fill the charger from the bottom of the slope i. e. the first flat battery put in the tray is the first one removed for charging. It is also vital that the correct charger is used.

The capacity of rechargeable batteries is normally specified at a discharge rate of a tenth or a fifth of the stated capacity. The capacity of alkaline cells is not specified in such an absolute fashion because the capacity varies significantly with the discharge rate. Unlike alkaline cells where the voltage reduces gradually as the battery is discharged the voltage of rechargeable batteries remains almost constant until the battery is almost fully discharged at which point it falls rapidly. This effect means there is often very little warning when rechargeable cells are about to run out.

One word of caution, most rechargeable batteries have a slightly lower voltage than the non rechargeable type and this can lead to two problems especially where several batteries are used. Some items may not work properly with the lower voltage - the number of these are becoming fewer and fewer all the time. The lower voltage can also mean that batteries need recharging regularly. Neither of these two issues have caused us any major problems.

There are devices on the market for recharging alkaline type batteries - my advice is avoid them at all costs, there are some potential safety problems. Never try and charge an alkaline battery in a NiCad or NiMH charger.

Always dispose of all types of battery properly and not with general household rubbish.