Battery Types?

[The Medway Handyman]

Recently got a catalogue from ITS London. On the page listing power tool batteries is the following, verbatim;

----------------------------------------------- Are you confused about the various battery types available? This information is a guide only, only batteries suited to your charger and specific tool should be used.

NiCD (Nickel Cadmium). Entry level rechargeable battery which must be fully discharged before recharging. Failure to do so can reduce battery life.

NiMH (Nickel Metal Hydride). These batteries have no memory effect therefore can be 'topped up' or charged at any time without affecting battery life. NiMH batteries also tend to out perform NiCD batteries in high drain applications.

Li-ion (Lithium -ion). The newest battery technology for cordless power tools, with no memory effect they can be 'topped up' with no effect to battery life. The main benefit to this battery type is the weight - up to

40% lighter that NiMH batteries makes these the favourite for power tools.

-------------------------------------------------

To a battery layman like me, this is a golden nugget of information. Makes it perfectly clear which is which.

So, first of all, is it by & large all true?

If so, should we steal it for the Wiki?

[Peter Parry]

(I've re-ordered this to make the reply easier to follow)

Not really. To call NiMH "entry level" is sales crap to get idiots to buy more expensive batteries. One advantage NiCd has over other technologies is it is rugged and works better at extremes of temperature.

NiMH and NiCd have very similar charging and discharge characteristics. NiMH batteries often come with better quality chargers and it is this rather than their fundamental characteristics which make a difference. NiMH have a slightly higher charge capacity than NiCd for a given weight.

So can NiCd with the right charger.

Wrong. NiCd can have better high drain characteristics than NiMH. It is a function of battery design not chemistry.

Just like NiMH and NiCd.

Not true, Lithium batteries have a finite charge cycle life and each charge, whether partial or full eats into it.

They are not necessarily lighter, they certainly have a better energy capacity per unit of weight so you can have the same weight and more energy or the same energy and less weight.

I'd rather something a bit more balanced.

[newshound]

NiCd seem pretty rare now presumably because of recycling and Cd toxicity.

I'd have said NiMH are now the standard, Li ion started in phones etc and are moving to tools, but at a price.

For individual AA cells in cameras and GPS, I get much better performance from NiMH than NiCd, but some of that is almost certainly thanks to using a better charger which does each cell individually. I agree with Peter that chargers have got better anyway and that tends to help NiMH.

I don't know whether the often described NiCd "memory effect" is true or not, but over time I've seemed to end up with more "bad cells" in sets of NiCd than NiMH.

[John Weston]

The memory effect occurs when NiCd is charged after a fixed discharge rate for a fixed time, as when charged by solar cells. When the time or load is random, as with power tools, it's not a problem.

"Standard" NiMH have a relatively high self-discharge rate, greater than NiCd. This means they lose their charge, at a rate of the order of

10%/month, when not used. There are now NiMH types (e.g. Sanyo Eneloop) that address this problem, with some 80%-90% charge remaining after a year on the shelf.

Li-ion doesn't have a similar high self-discharge rate, so is useful in tools that are infrequently used.

[The Medway Handyman]

I'd assumed that ('entry level') to be true, because all of the 'super deals' on DeWalt & Makita include low capacity (1.3a/hr) NiCD batteries, presumably because they are cheaper?

ISTR that Makita with red NiCD batteries were at one time called Maktek and offered as a lower cost alternative to a Makita with black NiMH batteries.

Is that so? I've always believed NiCD did have a memory effect.

Is this the crux of the matter? Is the charger in some respects as/more important than the batteries?

This is what I'm after Peter, the choice of batteries is very confusing for the average DIY guy, me included. I recently bought a new 14.4v NiMH 3.6 a/hr battery for my Makita DD because it seemed like a good deal. Truth be told I didn't really know if NiMH was a better or worse deal than NiCD.

So, to rephrase my question, could we have a section on batteries (power tool) in the Wiki to make matters clear for the battery numpty like me?

[js.b1]

Quality of cells is very important. Generic NiCad NiMH power tool batteries tend to be noticeably inferior to genuine Makita/Bosch. Generic or off-brand L-Ion laptop batteries can offer as little as 9 month lifespan compared to years on others.

I am dubious about L-Ion on power tools for the moment - there tends to be just 1 battery, charge cycle limit is finite, they cost a fortune, generics or off-brand might be significantly worse than branded for only a limited difference in eye-watering price.

Yes, if it means finishing a job a generic battery can be perfect. However even Pro cordless tools pale against even quite modest mains tools.

L-Ion is perhaps useful with 24V SDS monsters - where any weight saving makes them less unwieldy.

I'd go for a 3-battery special-offer vs 1-battery or more expensive 2- battery L-Ion.

[John MacLeod]

The observation on NiMH with regard to high-drain applications seems rather strange -- I'd reckoned that was one of the few things to be said for NiCd batteries.

However as things stand at the moment I reckon that the Li-ion technology is in practice the best all-rounder available. In my experience good Li-ion batteries can take a pounding for years. I use a lot of them -- quite a number of mobile phones, satnavs etc.-- and it's only one I've ever had to replace and that was after years of service and a mixture of charging regimes.

My Makita cordless drill is Li-ion. For me, the most relevant factor in that choice had to be that, since it wasn't going to be in use every day and might lie a month between uses, it wouldn't completely self-discharge if left lying, For someone using a power tool every day, that wouldn't be a relevant factor. In any case, it's Li-ion that seems to be the choice for top-of-range tools increasingly and that's where the development money is being spent.

My experience with Li-ion has been good all round. As, for that matter, has been my experience with ITS London (though that particular Makita didn't come from them). Nice guys who generally know their stuff better than most such operations when you talk to them.

[Dave Plowman (News)]

That is total bollocks. *Totally* discharging a Ni-Cad battery - ie one with more than one cell - is not a good idea. It should simply be charged when the performance drops off.

Memory effect is an urban myth.

No.

[Andy Dingley]

It's close enough that you won't be misled into bad decisions as a result.

One thing worth adding is Cd toxicity, and the imminent phase-out of NiCd.

[Peter Parry]

No, its one of the oldest red herrings going. It is possible to produce a loss of capacity in both NiCd and NiMH by consistently overcharging them but it has nothing to do with how far you discharge them.

Absolutely. Broadly NiCd/NiMH chargers fall into one of three groups. Firstly you have the ones which take a long time - at least 10 hours, to charge a battery. These treat the battery well and won't harm a battery if its only slightly discharged when you put it on them or if you leave it a few hours too long. Charging at 10th of capacity (C/10) is the safest way of charging but not terribly practical for tools in use all day.

Secondly you have the ones supplied with cheap battery tools. These usually charge in somewhere between 3 and 5 hours and have no charge regulation worth talking about. These are damaging to batteries and if left for more than a short time after charge is complete (as short as an hour) will often significantly damage them. The poor battery life on cheap tools is often a function of the poor chargers rather than the batteries.

Finally you have the well controlled 1hr fast chargers which monitor the battery state and modify the charging accordingly. Really good charge control is essential for LiOn as overcharging turns them into small explosive devices.

Basically if a battery is getting hot on charge it is being hurt.

We could certainly produce a chart comparing the characteristics of the various battery types. There isn't a single "best" one for all purposes. If we did no more than warn against the damage the cheap

5hr chargers do to batteries it would be useful.

[The Medway Handyman]

I've dealt with ITS a few times & found it a positive experience. They do some very good deals as well.

[The Medway Handyman]

Thanks Peter, very helpful.

[Clive George]

Is that really true? Are NiCds a lot less dense then? Eg AAs - what's the capacity of a good NiMH vs NiCd these days? (2500 vs 700 mAH?)

[Calvin Sambrook]

Totally discharging a Ni-Cd battery is one of the two ways to kill it (the other is of course poor charging) and the "battery conditioners" which were popular at one time which did this were one of the worst things you could do to them. The reason is that internally a battery consists of more than one cell in series and these will initially have very slightly different capacities. As the battery approaches total depletion the weakest cell will become reverse biased by its friends and this is *very* bad news, weakening it still further. Repeat this total discharge a few times and the weakest cell will eventually fail.

From a longevity POV the best thing you can do is to charge the battery when it's performace starts to drop off *using a high quality charger*. And thereby lies the rub, if you recharge at this point using a poor charger it will overcharge the battery and cause damage through that mechanisum instead.

There's an interesting back story to this which I've researched a bit and believe to be true. NiCad's do suffer from memory effect but, as others have said, only if repeatedly charged and discharged at the same rate for the same time. There are good chemical reasons for this which I won't go into here.

Now this effect is of course unobservable in normal daily life because they are never used that way but when NASA started using them in space that's exactly how they were treated. The charge/discharge cycle is dictated by the orientation and trajectory of the spacecraft (ie. how its solar panels align with the sun) and tends to be highly routine and the drain tends to follow set patterns. NASA had to go away and discover how and why their batteries were failing, which they did, and when they made this known the manufacturers and the public saw it as the reason NiCad's died, missing the detail and blaming memory effect rather than the crap chargers for killing batteries.

[Peter Parry]

Both have similar characteristics as far as their chemistry is concerned. Because NiCd are due to be phased out there has not been much development of them for a few years. As a result new manufacturing processes are being seen in NiMH giving better capacities for the same battery size. That said "capacity" figures need to be treated with caution if you don't know the discharge regime they were tested under. I've had NiCd 1AH batteries which had better capacity than 2AH NiMH in one particular application.