Batteries

OK, so we all know cordless power tool batteries have a limited life governed by the discharge cycle.
What's the best way to prolong life? Discharge completely on a regular basis? Recharge immediately after each use?
And where does one get the individual cells from if you want to replace?
Dave
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If your tool does not have a low-voltage cut-off, then do not use it once it starts to fade rapidly. This will reverse charge one or more cells, and do terrible things to the life. For both NiMH, and NiCd, occasional deep discharges are not a bad idea. http://www.cpc.co.uk/ has cells.
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David Lang wrote:

If you can do a full charge discharge cycle most of the time this will help. If you start out with a good quality pack this is easier to do anyway since the self discharge rate will be low, so you can use half the charge, put the tool down, come back a week later and still use most of the other half. Many of the cheaper packs encourage partial charging on the grounds that you need to charge packs in an unknown state just the be sure they will be ready when you want them.
Not overcharging is one of the most important things. With most NiCds you can charge at a low rate (i.e. 16 hour charge) and not worry too much about going over. Obviously this is not much use for a power tool though - most people want faster chargers. The worst examples are the "mid speed" ones - often these will charge in 2 to 5 hours and have no control over the charging. These will kill batteries fast. A good intelligent charger with delta peak detection and thermal sensors will work best.
Don't run packs completely flat. Don't leave them flat for long periods. Don't subject them to extremes of temperature.

RS / CPC/ Farnell / Maplin / and any decent model shop.
Failing that send the complete pack to http://www.re-cell.co.uk/ and they will rebuild it for you.
If you equip a poor or medium spec tool with a decent set of cells and buy it a good charger (Makita and the like sell them separately if required) you will not only get much better life from the batteries, but also improve the performance of the tool by sometimes a very substantial margin.
(I note that many budget tools have copied the same terminal arrangement as used by Makita, since their chargers are universal and will typically charge anything in the range of 7.2 to 14/18/24V (depending on model) you can often use a Makita charger on these other packs as well)
--
Cheers,

John.

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1/10th capacity charge rate for 14 hours and use a timer. They should only be discharged to the point where the performance suffers - not completely. Fast charging may reduce the number of packs you need for any one heavily used tool, but IMHO still reduces life no matter how well done.

Any electronics supplier like Maplin, RS, CPC etc. Maplin own brand tagged cells are pretty good - although my favourite make is Sanyo.
--
*Growing old is inevitable, growing up is optional

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Sat, 30 Jul 2005 23:14:23 GMT, David Lang wrote:

Self discharge is one of the most damaging things for NiCds, note that come discharged. If you know your are not going to use the tool for a period(*) then it's best to take the charge level down low, but then of course you need to charge it before you use it. No more whip it out and off you go...
As I want the convience of instant use I always charge when flat, I don't do partial charges.

Others have mentioned the big general suppliers but there are a quite a few smaller battery/cell specialists out there that offer competative prices and my well recell for you. Recelling might not be as straight forward as it looks, especially if the case is welded together, rather than glued or screwed. Yellow pages, batteries are heavy so postage high.
(*) Months rather than days or weeks but it depends on the quality of the cells. Some will self discharge completely in a couple of months others much longer.
--
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What do you mean by this? Discharging deeply harms cells, by reverse charging them. Sustained charging converts one of the metals in the battery to a different form, and makes it harder to discharge rapidly. Self-discharge does not harm cells.
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Yeah. Right. That'll explain why the Nicads on my 144MHz and 432MHz handhelds, which have been sitting on a shelf for 10 years, are as dead as doornails.
--
"The road to Paradise is through Intercourse."
[email me at huge [at] huge [dot] org [dot] uk]
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Self discharge, unless they go totally flat for long periods does not harm cells. This does not seem to be what the Dave was saying.
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[The sound of goalposts moving]

Nicads also self-discharge very quickly.
--
"The road to Paradise is through Intercourse."
[email me at huge [at] huge [dot] org [dot] uk]
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No, they don't. NiMH cells self-discharge very quickly. NiCd cells left on the shelf at room temperature for a year will have a significant amount of charge left.
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[34 lines snipped]

As you wish. Not that I shall pay much attention to anything else you post.
--
"The road to Paradise is through Intercourse."
[email me at huge [at] huge [dot] org [dot] uk]
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It's got very little to do with what I wish, and much to do with the contents of datasheets, and the performance of batteries in the real world. For example http://www.gpina.com/pdf/70AAST.PDF Specifies that their batteries will beat 20% per month charge loss in the first 28 days.
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiCd_Overview.pdf
Specifies that at 6 months and 20C, it'll have 75% remaining, at 0C, 85% remaining after 6 months. Extrapolating the graph out to 12 months, maybe 45% at 20C, or 60% at 0C.
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiMH_Overview.pdf
Is the corresponding document for NiMH, and gives approximately similar results - but with weeks replacing months in the time axis.
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http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiCd_Ov erview.pdf
To be fair you are not only quoting from arguably the best manufacture as opposed to the sometimes-doubtful quality of some OEM batteries, but also in NEW condition. After a year or so of charge cycles they do self-discharge at an ever increasing rate. IMHO of course :-)
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Not IME.
At least for AA cells, I've found that they almost always have charge in even after a couple of years. (specifically, a radio in the attic, and one in the garage, that I know has been up there that long still worked) And the cells have mostly been in use since 1995 or so.
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On 31 Jul 2005 16:44:31 GMT, Ian Stirling wrote:

Read what I wrote. "... take the charge level down low, ..." nothing about a deep discharge. No lower than an average 1v/cell for the battery. Little risk of reverse charging a cell at that level.

Who mentioned sustained charging? I didn't.

Quite. I've got lots of dead NiCds that died on the shelf, doesn't really tally with "Self-discharge does not harm cells." does it...

Would you like to come and talk to the cells here that died within 6 months and were pretty naff after 2.
Latter you witter on about what the spec sheets say. What are the full test conditions? I suspect the spec sheets quote a nice fresh cell straight from the factory carefully and slowly charged in a strictly controlled manner and then left in a controlled and stable enviroment.
Not a cell that has been bumped, charged, partially discharged, over charged, deep discharged, partially charged, discharged, fully charged then left on the shelf in an ordinary room. That is a real world cell in average use in a power tool with a cheap charger.
--
Cheers snipped-for-privacy@howhill.com
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No, you diddn't say that.
However, that paragraph made no sense to me, which is why I was trying to get you to clarify what you meant.
Self-discharge occurs from the time the cell is made, to the time it reaches 0V. It's the result of various parasitic electrochemical processes inside the cell, due to compromises in the construction, impurities, and the basic design, and you can't do anything about it. Do you simply mean age?
And I've never seen in any manufacturers data, charger design notes, or books about NiCd, any reference to high state of charge being detrimental to life.
Overcharge, reverse charge, discharging and recharging, rapid charging, rapid discharging, high ambient temperature, can all be detrimental to cell life.
This is different to Li-ion, where high cell voltage is indeed a big factor in aging, as it degrades the electrolyte. This doesn't happen with NiCd.
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wrote:

I seem to recall reading somewhere that a car battery will loose around 15% of its charge per month if the battery is just left sitting.
Graham
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It very much depends on the quality. I've got a 7.2 volt drill kept for electronics stuff (clean ;-)) which was re-celled with Maplin's finest ages ago and hasn't been charged this year. Worked fine yesterday.
Rubbish cells - or damaged by poor charging - can self discharge in a few days.
--
*Forget the Joneses, I keep us up with the Simpsons.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Huge presented the following explanation :

That will be due to the crystalline growth which can short circuit the cells internally. A brief application of a high current source across a cell will blow the short circuit away [1] and the cell can then be charged once more.
[1} A safe way to do this is by charging up a large capacitor and connecting it across a shorted cell.
--

Regards,
Harry (M1BYT) (L)
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