NiMH Batteries

...I would have to get NiMH (Nickel Metal Hydride) rather than NiCd (Nickel Cadmium), as they have a higher capacity.

So what is the advantage of NiMH over NiCd?

A NiMH battery has a 30% higher capacity than a standard NiCd battery, which means of course that it lasts longer between charges. Furthermore whereas NiCd tend to suffer from “memory effect” – in other words the batteries “remember” how long it took to discharge ...
...is not a problem in NiMH batteries in any case, although it can be worth periodically discharging batteries fully, rather than just recharging when you think they are dead.

There is another performance affecting problem in NiCd which also doesn’t affect NiMH known as crystalline formation, whereby the materials in the battery which are present in crystalline forms start to grow, which cause a loss in performance from the battery, ... more

I had always thought that a rechargeable battery was a rechargeable battery, but I was proven wrong recently. I really discovered that there were two types of rechargeable battery having purchased a brand new Minolta Dimage 5 digital camera (op to follow soon!). I had just spent near EUR 1100 and was therefore somewhat taken aback that there were no rechargeable batteries supplied with it, just a set of alkaline batteries. Fortunately when I bought it, the shop assistant did say that I would have to get rechargeable batteries separately and that I would have to get NiMH (Nickel Metal Hydride) rather than NiCd (Nickel Cadmium), as they have a higher capacity.

So what is the advantage of NiMH over NiCd?

A NiMH battery has a 30% higher capacity than a standard NiCd battery, which means of course that it lasts longer between charges. Furthermore whereas NiCd tend to suffer from “memory effect” – in other words the batteries “remember” how long it took to discharge previously, and therefore gradually lose performance by not fully discharging. A lot of battery chargers also have a discharge function to avoid the memory function, but this is not a problem in NiMH batteries in any case, although it can be worth periodically discharging batteries fully, rather than just recharging when you think they are dead.

There is another performance affecting problem in NiCd which also doesn’t affect NiMH known as crystalline formation, whereby the materials in the battery which are present in crystalline forms start to grow, which cause a loss in performance from the battery, and in extreme cases electrical shorting of self-discharge at an accelerated rate.

The higher capacity is particularly useful if you are using things like digital cameras which have a thirst for batteries. Take the Dimage 5, which only got 6 pictures at highest resolution out of 4 non-rechargeable AA batteries and 4 out of rechargeable NiCd batteries, whilst getting nearly eighty(!) shots out of 1800mAh rechargeable batteries. Whilst normal alkaline batteries (your Duracell/Energizer/Varta ones) perform better than NiCd batteries, due to the fact that their capacity is 1500mAh compared to 1200mAh, and they also benefit from the fact that they lose their charge gradually rather than a sudden drop off – something I remember discovering in a physics practical where we attached a voltmeter to a computer which compiled the data and drew graphs, the NiMH batteries have a still higher capacity – either 1600mAh or 1800mAh and therefore have a longer life (physics lesson over!)

Ecological impact of NiMH batteries compared with NiCd:

Whilst alkaline batteries are Mercury (Hg) and Cadmium (Cd) free, both of which substances are toxic and can erode into soil, NiCd batteries contain the cadmium, meaning that they should be disposed of properly (in Austria you are recommended to return the batteries to the shop when you go in to buy a new battery – a cunning sales ploy but also means that there is less risk of Cadmium seepage), whereas NiMH are classed as being environmentally friendly because their level of toxic metals. (biology/ecology lesson over!)

So on to the consumer side of the review – who make NiMH where can I get them from?

NiMH batteries are increasingly easy to get hold of, and are available at most chain electrical stores, with many of them packaged with chargers and with packaging including things like “Ideal for digital photography” – i.e. usually 1600/1800mAh batteries.

A few places I have found them on the web are as follows:
http://www.eurobatteries.com
http://www.mx2.org
http://www.battery-box.co.uk
http://www.maplin.co.uk

Some makes of batteries to look for:

Ansmann (German brand – have been very pleased with them)
GP
Sanyo
Millennium
Varta
Uniross

Of course the most important to look for is not the name, but the capacity. For digital camera use, use at least 1600mAh batteries. The higher capacity batteries might be more expensive than the lower capacity batteries, but it would be a false economy to buy lower capacity batteries, since you will only have to recharge them more often, and the saving is therefore negated. Of course their use is not exclusively reserved to digital cameras, and indeed using NiMH batteries rather than NiCd ones in everyday appliances makes considerable sense, as the initial outlay for a set of four high capacity NiMH batteries and a fast charger (i.e. 2-3 hours) will soon become a saving – in the case of a digital camera you are probably in profit from the first charge onwards, and of course by re-using two sets of batteries you are doing your bit for the environment rather than getting through alkaline cells left, right and centre.

PS The boxes below do not make sense - please ignore the size one! 

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