best charger for nicd and nimh batteries

[Fred]

Hi,

I was wondering about using rechargeable batteries for our children's toys. I know that rechargeable batteries are suited better to some applications than others; do you think they would be suitable for these? I think it is only low drain uses, such as clocks, where rechargeables don't perform well, isn't it?

What is the best charger to buy? I thought Uniross was supposed to be the name in rechargeable technology but I've read a few reviews on amazon of their charges and they are criticised for being timed chargers rather than intelligent chargers. The energiser charger appears to be highly recommended though one criticism is that it only charges pairs of batteries and many toys use three at a time.

Is there an intelligent charger than charges batteries individually?

I'm likely to buy nimh. Why are these preferred over nicd? Is it just that cadmium is not friendly? Is there any advantage to ever using nicd? Would one charger charge both if I ever needed or are some chargers nicd or nimh only?

Finally, I see that AA batteries are rated at 2700mAh and C and D cells are rated 2600mAh. I would have expected a larger battery to have had a higher capacity; why not?

Thanks in advance.

[Bruce]

NiMH batteries tend to have higher capacity. NiMH batteries seem to last longer. NiCad batteries duffer from an earlier reduction in capacity than NiMH.

Some "intelligent" chargers will charge both types.

You can buy higher capacity C and D cells in some brands. In other brands, they just put an AA cell inside a C or D size casing.

[Gareth]

I think you can get dummy cells which will allow you to charge one cell at a time.

NiCd has a lower internal resistance and can be better for applications which require high currents for a short durations (e.g. cordless drills) However even here they are being phased out. NiCd also works better at very low temperatures (well below freezing), but that isn't likely to be an issue with toys.

For most applications NiMH is better.

[D.M.Chapman]

Pretty much. A big problem with NiMH is the self drain - they will got flat on their own with little use. A low drain device you'll find the cell goes flat on its own before the device flattens it.

Look for the Eneloop (and clone) type cells - *much* better. They appear to be lower capacity but with a few days the normal ones will have dropped to that level anyway.

Find one that charges individual cells with decent feedback.

Plenty. Not cheap but worth the extra IMO. I use a couple of Ansmann chargers. Take a look at the Energy (plus) range for example.

I'm likely to buy nimh. Why are these preferred over nicd? Is it just

Any decent charger will do both.

Because they are AA cells in the large empty plastic case. You can get adaptors to do this yourself which is a lot more flexable (not sure the ones that take more than one cell are wise - uneven discharging could be a problem).

Proper NiMH C and D cells are available, but are usually expensive (check Lidl for cheap ones - although I've had issues with them). Take a look at

:-)

The other thing is in practise you'll find a decent brand 2300mAh cell will often be much better than a cheap 2700mAh - I've given up with "cheap" cells.

Darren

[AlanD]

> >>I'm likely to buy nimh. Why are these preferred over nicd? Is it just

> >> > Pricey :-)

Another vote for Ansmann here - I've got several of their chargers, all excellent.

I've had good service from Budget Batteries in the past:

[mick]

Rechargeables are not always the best choice.

1) You shouldn't run them flat. They really need to be recharged *before* they go flat.

2) The terminal voltage is lower. Both NiCd and NiMH are 1.2 volts and alkalines/ordinary cells are 1.5v (nominal - they start higher than this). This *can* cause problems in some equipment as they may be detected as flat when, in fact, they have a lot of charge left.

3) NiCd and NiMH have an interesting discharge curve, where they hold their voltage up right until the end then go flat quite suddenly, without any warning.

4) NiCd & NiMH have a low internal resistance, that is they can provide a very large current for a short length of time. If they are used for motors, for example, then some protection is needed against the motor being stalled as the resulting high current could permanently damage the motor.

5) Nicad & nimh are temperature sensitive. As the temperature falls the cell *appears* to have a lower charge and will go flat earlier. If the cell temperature is raised then the full charge reappears!

Choice of chargers can be a minefield. Basically, you exchange charging speed for cell life. Fast chargers shorten the life of the cells, safe chargers let the cells last longer. There isn't really any need to charge cells individually in many cases. A lot of equipment uses 2 cells so you can charge quite satisfactorily in pairs. There are intelligent single cell chargers, but they aren't cheap. Look for delta-V (if possible) and cell temperature termination, probably with a safety timer, in any charger. I doubt if Uniross are any better or any worse than any other company! It's difficult to judge without testing a lot of different chargers with a lot of different cells.

Cell mAh values can often be taken with a pinch of salt. They are rarely accurate and much depends on the characteristics of the charger and the load as to how much useful charge a cell will accept. I've had 1800mAh cells that outlasted 2200mAh cells in a camera - by a large margin too. I'm not the exception either.

Having said all that, I would first check the toys' instructions. Some specifically tell you not to use rechargeables. Sometimes this is for safety reasons and shouldn't be ignored. Any others would be worth a try, but you may get less "playing" time between charges than you get with ordinary batteries.

[Dave Plowman (News)]

Not so with any of the power tools I have. And not a problem with toys, surely?

[Dave Plowman (News)]

Keep an eye on Lidl special offers. They do a very good intelligent charger that takes all sizes and types - and charges them individually. Takes 6 AA or AAA or 4 C or D at the same time. Two PP3. Costs about a tenner. Their cells are good value too.

[Michael Chare]

See

have always been fascinated by this but I have no practical experience.

The GP ReCyko batteries sold by CPC claim to hold their charge better over a long period.

[D.M.Chapman]

Seems to be with plenty of the AAs I've got. The eneloop types seem *much* better. Loads of toys get played with for a bit, then forgotten about for a few weeks. Batteries often flat when toy rediscovered a month later.

Maybe it's just the crap ones? I'm guessing you have half decent powertools?

Darren

[Douglas de Lacey]

I have an Innovations (rememeber them?) recharger which was claimed to recharge standard alkalines as well as NiCds. Works pretty well on both and I'm sure I've seen something similar recently.

Surprised no-one's mentioned 7dayshop: they have a range of smart chargers.

Douglas de Lacey

[Dave Plowman (News)]

I suppose they are. But I also use NiMH for this keyboard and mouse and keep a spare set charged ready for use. They need changing about every 6 weeks - which means the self discharge rate is miles better than 6 weeks. The cells I use were bought from Lidl.

[Dave Plowman (News)]

Those claims have been refuted. Unless you 'recharge' the alkaline long before it is exhausted. In which case there's little point in using them given how cheap proper rechargeables are now. Unless you need the 1.5 volts.

[Mark]

Maha C401FS for AA and AAA batteries.

[Douglas de Lacey]

Hi, Dave, I was hoping someone would bite as I was never able to find any hard data about them. My own experience was entirely heuristic: run my radios till they stopped working, replace batteries with a recharged set and recharge the dead ones. Worked fine for years. Remember this was in the very, very early days of rechargeables, but I still have a coupla alkalines still working after many recharges. Nowadays I agree there's virtually no point.

I'd be interested in seeing a more scientific evaluation if you have a reference lying to hand.

Douglas de Lacey

[Dave Plowman (News)]

No - it was my memory of a Which test. They found if an alkaline was discharged to the point where its performance had noticeably suffered - as most do with any cell - it could only be recharged to a tiny percent of its original capacity.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Dave Plowman (News)" saying something like:

Can't get much lower drain than a clock or remotes. Bog-standard NiMH cells will last six weeks in a Sky remote (in full-on use) before the 'low battery' warning comes on and then they'll last for ages further - or until you get fed up being nagged by the stupid nag screen. Similarly, b-s nimhs will last for up to six months in a small shelf clock - and these are ancient ones I keep just for this application. So, it seems that as long as there is *some* current drain, the ordinary cells last much longer than just sitting idle.