Do I need to turn battery chargers off?

Not many years ago, electrical equipment was pretty well fixed in position by a cable with a plug in the wall. Now we expect to carry everything around with us and to be able to use it anywhere, but this needs batteries and batteries need charging, so we have a box full of different sized and shaped chargers and have to keep remembering to charge each device regularly. There are many different types of batteries, but most of them store low voltage DC (direct current) electricity, whereas mains electricity is high voltage AC (alternating current), so a battery charger has to convert from one to the other and this unfortunately means a loss of efficiency. If you feel a battery charger while it is charging it's warm, and that heat is wasted energy, so if we want to reduce our energy consumption and carbon emissions we do need to be careful about how and when we use battery chargers.


What kind of chargers are there?

Leaving aside car battery chargers, which charge big lead acid batteries, many small devices like phones, MP3 players and some cameras have batteries built in, and the charger just plugs straight into the device. When the battery is fully charged however there is still some electricity being used, so it's important to unplug it as soon as you see it's finished. Chargers for rechargeable batteries - the usual AA or AAA type - often have an 'intelligent' control which senses when the battery is charged and switches itself off, so if you're buying one make sure it has this control. Increasingly though small devices can be charged through the USB port of a laptop or desktop computer, which gets round some of the energy losses from a normal charger. Finally and best of all from an energy point of view there are solar or hand driven chargers. Solar chargers will take much longer then the mains equivalent to fully charge a battery, but if you plan things so you always have a spare set of batteries in the charger you can have a constant supply of fully charged batteries at no cost at all. You can get solar chargers with connectors for just about every kind of device, often designed specially for travellers.Hand driven chargers are useful for emergencies in remote locations but are unlikely to be used for everyday purposes.


How can I make the batteries last longer?

The standard type of rechargeable batteries are now mostly NiMH (nickel metal hydride) which may suffer from something called the 'memory effect' which means a battery can take less and less charge over time and discharges quicker. The way round this is to run the battery to empty about every 30 charges which helps it keep its full charge. Lithium ion batteries, which are used in phones and many other devices now, don't suffer from this effect and in fact last longer if they are kept frequently topped up. If the device they are in has a display showing how much battery power is left however, it will become increasingly less accurate unless the battery is again full discharged every so often. So it looks as though whatever type of battery you are using it will last longest if occasionally allowed to run down to nothing.

If you're interested in more technical information about battery charging, the wikipedia page is good - http://en.wikipedia.org/wiki/Battery_charger#cite_note-ProlongLith-17, as is this webpage - http://www.batteryuniversity.com/parttwo-34.htm.