Thread: Discharging cordless drills before recharging.

Lets see what I know to be facts.

Almost without exception, battery manufacturers documentation and every text on batteries I have read states that discharging a battery past a certain point will cause damage and shorten life.... leaving a discharged battery connected to a load for any period of time is universaly acceptad as unhealty for a battery.
So without question discharging a battery stone flat it not recomended.


Almost without exception manufacturers documentation advises against idleness in all battery types.
So if you are going to have a rechargeble battery or a rechargeble battery powered device it should be cycled..... charged and discharged on some sort of regular basis. How deeply will also depend on battery type.
Lead acid batteries for example strogly resent deep cycling.
Exactly how regular will depend on a variety of factors, but it would be reasonable to say once a month would be healthy.


Almost without exception battery manufacturers and suppliers of rechargable battery powered equipment recomend and extended first charge and advise that the battery may not perform to capacity untill a number of cycles after presale storage.

One other thing is certain
Battery technology has moved forward and all the manufacturers certainly have been trying to improve battery performance, both within established battery types and by devising new types.

all this I know from documentation

I know in the past.
I have taken NiCad batteries "used by others" who have habitualy short cycled them, and achieved plainly noticable improved cycle life, by giving a number of deep cycles.

some examples
aerial installers who would do up to 8 calls a day & would charge their drill battery at every stop.
Video cameramen who would charge all their batteries, regardless of their state of charge every day on return to base.

Technicaly a powertool application will be considered a heavy application. however if it is a drill/ screwdriver used only for light work (A blind & curtain installer for instance) the load will never be heavy and the discharges will be short and infrequent in comparison to other uses.

there may also be other problems masquerading as discharge memory.
for example
NiCad batteries do not hold good charge for extended periods more so fast charge types.... they self discharge quite rapidly.

Friday: "I charged this piece of ribbish last week & havnt used it since & now its flat after 5 min"....... yeh so.

After not usong a battery drill for 6 months: "This thing's flat & I just chardged it an hour ago.... battery must be stuffed"..... NO probaly not.

For most people who regularly use their tools and don't habitulay short cycle their batteries none of this discharge memory thing will ever be an issue.
Particularly with inprovements in battery technology, and improvements in charger technology being offered.

Also take powertool manufacturers recomendations with a grain of salt.... they are most interested in getting their tool past the waranty period.
So ifv thy find they are gettin significant claims from users who are discharging to stone flat they will recomend against discharging at all.

As for guaging the state of discharge by the behaviour of the tool off load.... this is most unreliable because as the terminal voltage drops the motor current draw will also drop inproportion & the friction of the gear train and the internal resistance of the battery come into play....you could spend weeks analising that lot & then not get it right.

If you want to be pedantic you need to measure the terminal voltage.
Now this is what all the real good chargers do.....
As it has been said a good charger is well worth it.

However if we are talking powertools.... you are mostly stuck with the charger that came with your tool.

anyway
cheers

So without question discharging a battery stone flat it not recomended.

That's interesting. I'm certain that the manual that came with my mobile phone and at least one or two others I can think of recommends letting the battery go completely flat every few charges. The manual for my Panasonic cordless phone says very clearly that once every couple of months you should unplug the phone and turn the handset on and leave it that way until it goes flat. So what's going on there, different type of battery?

Always amazes me how truths are buried. I mean, all the cabinet makers I know believe that Nicads have a 'memory'.

Apparently the problem only existed for batteries in Satellites where they would be in the sun light for half the time and darkness for the other half as they did an orbit of the Earth. They were charged by solar panels.

Yeh remember manufactures instructions and a grain of salt and the behaviour of the appliance not being a reliable indicator.

the phone will probaly "fall over" at a certain point and appear to be stone flat where in fact the battery may still be at an acceptable discharge point.

Also consider the size and cost of a cordles phone battery is much less than a drill battery pack.... the charger circuit is probaly crude too.
We get nowhere near the life out of our cordless phone batteries that I get out of my drill packs.
Realy it is a very different application..... if that matters.



Discharge memory in nicads is most certainly a real issue.

The textbook situation is where a device is discharged to a specific point well short of a full cycle and is then recharged.

the satelite example ( real or not) would be a good example, identical discharge period and load on a repiticious basis.

Another is a radio mic used in a church with a fixed service length.
the battery is charged after every service which is a fixed length... after some time the battery won't last a whole service.... cycle it deep & hard a few times & all is well again (well almost).... Don't start me on inappropriate uses of rechargable batteries.

Discharge memory is problay more a convienient way of explaining a far more complicated technical reality.

Batteries particularly "dry cell" type batteries are far more complicated and less ideal things than most people would hope.

One of the major hurdles for dry cell manyfactuers is to get the chemicals and stuff within the battery to behave consistently and dristrbute them selves evenly as the cell charges and discharges. Failure to achieve this causes all these problems.

regardless of all said previous
The ocasional full and proper discharge of a NiCad and a following properly managed charge will not harm a NiCad and there is strong evidence that it does help both performance and life expectancy.
NiMh certainly wont object either.
This can probaly be achieved with use in most power tools.
And with modern battery fromulations its probably less of a problem than it once was.

I seem to get the idea that this discharge issue has got out of proportion generaly.
More important is
using the tool regularly and moderately
keeping the batteries cool & /or allowing them to cool
and
charging them properly in the best charger available

Also rember that this type of battery has a finite number of discharge cycles.
So adding too many "regular maintence discharges" will certaily reduce the life of the battery.


cheers

From memory (excuse the pun!), in NiCds, the memory effect occurs under low-rate charging and discharging and is due to large crystals (with relatively low surface area) forming in the battery. The cure was simple - high-rate charging and discharging to breakdown the large crystals into smaller crystals (with more surface area). The surface area increase gives more usable capacity and the battery "recovers".

In power tool applications, low-rate cycling is not evident and not a problem.

Well I'm still confused.

Its sounding like one of those things where only slight improvements are made by adhereing to one rule or another. uno, hardly worth the effort trying to remember when to charge a certain way etc (or not?)

See, I just want a simple process to remember..........and one can't trust the documentation that comes with it apparently.

Soundman.....how would you go about re-charging a brand new makita 14.4 Nicad drill , when it starts to sound sick whilst driving a screw ? Just drop it back in the charger and not worry about that memory business ?

And, after a period of time. And its getting quite old, some months down the track, do I consider charging it a different way ?

We've got an 18V makita drill too. Nicad. Treat it the same I'd guess ? yes ?

Whether it be the claimed " metal creep" problem or this "crystalisation issue" as mentioned, its all irrelvant to the argument.

the fact is reduction in cycle life due to incomplete cycling ( or other reasons) is a real problem that I can say I have witnessed in both low and high rate charge & discharge batteries.

10 to 15 years ago when NiCad was an awfull lot more expensive than it is now...... we would do anything that worked to prolong the life of a battery pack.

I can remember pulling battery packs apart, testing & cycling individual cells and reassembling them leaving out the hopeless cases..... just so a few extra months could be got out of some packs.
At that time the sony packs that all their pro & semi pro cameras used were hundreds of dollars.

So don't try & tell me memory or some other cycle reducing desease dosn't exist..... because it does..... in both high and low rate applications.....I've seen it, I've measured it & I've been paid to deal with it.

Don't assume that all power tool uses are high rate because they aren't.
If the tool duity is low and the load is low... it will be low rate
If the chrarge cycle is short or light It won't have a chance to help the problem.


so having established that the problem exists
I will again state that I don't think that it would be anywhere as big a problem as it once was..... for a variety of reasons.

Now
I have never seen this problem in newish batteries.... it takes time to "build up"..... I would have seen this in batteries that had some age or use behind them. (apart from batteries comming out of storage)

So my reconing is this
when you buy a new battery (or tool with)
Charge it fully immediately
Give it some moderately stiff use till it reasonably need recharging
So charge it
Check it your self.... it should pick up some schnaps over the first 2 or 3 cycles
Now this sounds very much like normal use to me.

once it is starting to get some age... 6 months or so of "trade use"
you might thing about a couple of deep cycles


normaly you wouldn't bother till it starts to lack holding power.

consider this too if you are a weekend hack and havn't used the thing for 6 to 8 weeks or more
a/ it wont have held the charge all that time
b /it is comming out of storage.
this isn't a memory problem or whatever.

now when the battery is getting old and tyred it is very much worthwhile doing something to spark it up a bit.... what have you to loose.

first port of call is the freezer... clean dry ziplock baggie... into the freezer over night... and a full charge in the morning.
you might then want to give it a few heavy charges & discharges.

In the past there were all sorts of " remidies".... the high voltage treatment was popular.... slapping 50V DC across the battery....." to blow the metal creep away"...... Hmpf never had any sucess with that one at all & killed off a few half dead cells trying.

So with new batteries ...... use them normaly.

now about use
Builders.. being builders...... will recgharge batteries when they wont drive happily any more.....yeh right........ they wont bury a 6" batten screw in hardwood so it must be flat.
This is not a reasonable charge cycle......If it wont bury a 1" chipboard screw in radiata...... that is reasonable for being in need of a charge.
do you get me

As I say with reasonable use, considering modern batteries and chargers I don't think it should be a problem for most people.
So to that extent the problem dosn't exist...... Hmmm


Now back to the cell reversal and mismatched cell issue from a while back.
In the past all "reputable" battery packs were made from batch matched cells.
the packers would load a pile of cells up in a gismo and test their load capacity and charge characteristics and grade the cells so the cells in an individual pack had matched characteristics.

No I dont hear much of this these days... either the cheaper stuff thay don't care about & don't mention.
or
the manufacturing process is better andmore consistent....

or perhaps both.

back when I was inclined to do so... I pulled apart every failed battery pack that came my way and tested all the individual cells... in the hope that it could be saved.
Yep I found plenty of dead cells and plenty that the cells in the pack were realy badly matched.
However this was only in realy badly flogged packs & none of those would charge properly at all. & generaly if one cell was dead... the rest were prety donged anyway.
I have never seen thuis level of mismatch in a pack that was just weak or sad.

All sorts of people get precious about various causes and effects that could theoreticaly be a problem, but as long as you do the reasonable thing NiCad's particularly the large high rate ones are pretty robust and you have to do "unreasonable" things to the to cause a short term failure like forcing a fatal reversal of a cell.

Again.. sensible reasonable use and keep them cool.
The odd deep cycle won't hurt & may help, but there is no point deep cycling on a weekly basis.

cheers

Originally Posted by soundman

Whether it be the claimed " metal creep" problem or this "crystalisation issue" as mentioned, its all irrelvant to the argument.

With respect Soundman, these are two separate problems with two separate causes:

"Metal creep" is a wicking or dendrite like growth due to separator failure or the chemical composition of the battery (chemical additives are usually added to prevent this wicking formation). This causes the cell to short out.

"Memory effect" I briefly explained in a previous post, is usually due to low-rate charging (i.e. 16-hour or "trickle" charging). It causes the cell to loose capacity.

I'm not arguing "memory effect" doesn't exist, but it is unlikely to be evident in power tool applications. (which will flatten within an hour of use and often are recharged within an hour of charging).

Treat them as "irrelevant" if you wish, but I like to try and understand things myself.

I can't sit back and ignore these discussions. Listen to Soundman - he's got it right. It matters not if you're a Tradie or a hobbyist and you recharge often or seldom or the cells are new or old. The key for Apricot tripper is to re-charge a battery pack when it loses its oomph. NiCd does develop "bad" capacity-memory if you don't charge for the optimum length of time.

Sadly, there are so many cell capacities and load ratings that it's almost impossible for the layman to determine the optimum charge time from "flat". I have a cheepie Ozito pack that's NiCd and a has a cr@#p Chinese charger that won't cut out when it's full, so I had an electronics mate determine the optimum re-charge time from full discharge (3 hours) using quite sophisticated monitoring equipment that most people don't have. I fitted a cheap Woolies timer to teh charger so now I can keep these cells healthy. Sorry Apricottripper but it aint easy and there's no universal answer for NiCds except that :

1. Batteries hate heat!
2. Batteries don't like impact like being dropped.
3. Battery packs fail when a single cell fails to reach full charge and most people can't rejuvenate a single cell in a battery pack. I've done it and it requires soldering and cycle-charging and re-assembly - a real PITA.

Listen to Soundman - he knows!

....and if you have a Makita 9.6v 2ah NiCd battery pack with a really good Makita charger that cuts out when the battery is fully charged, the battery packs will last for 10 years, as mine have. And it's a complete no-brainer.

Originally Posted by Knurl

I have a cheepie Ozito pack that's NiCd and a has a cr@#p Chinese charger that won't cut out when it's full, so I had an electronics mate determine the optimum re-charge time from full discharge (3 hours) using quite sophisticated monitoring equipment that most people don't have. I fitted a cheap Woolies timer to teh charger so now I can keep these cells healthy.

The odds of getting good battery pack life when using a cheap non-regulated charger are very slim. Any charger that has to be manually switched off after a stated period of time is bad news. These are usually the same chargers that state not to recharge the battery unless it is flat. Why? - because these chargers are incapable of monitoring the state of the battery and simply recharge at an approximate constant current (A) and the users controls the time (hr) until the approximate amount of charge (A-hr) has been returned to the battery. If the battery isn't completely flat it will be over-charged and its life shortened. Also, during the "fully flatening" process there is the risk or cell reversal which is probaly the quickest way the kill a battery pack.

The other major problem with this type of charge is that there is no "equalisation charge" phase at the end of the charging. The lack of the equalisation charge will result in the cells in the pack becoming more and more unbalanced each time it is recharged. This will eventually lead to a cell reversal within the pack during use and result in pack failure. This will be more prevalent in higher voltage packs so an 18V pack will be more troublesome than a 12V pack.

The idea of the timer (as in the above quote) will help with the over-charge but it would be better to have an equalisation charge as well.

With a good charger, there will be no issues with leaving the battery in the charger indefinitely and it would be a good idea to do so periodically to allow a full equalisation charge to take place. This will take much longer than the stated recharge time.

Chris

Originally Posted by soundman

there may also be other problems masquerading as discharge memory.
for example

After not using a battery drill for 6 months: "This thing's flat & I just chardged it an hour ago.... battery must be stuffed"..... NO probably not.
For most people who regularly use their tools and don't habitually short cycle their batteries none of this discharge memory thing will ever be an issue.
Particularly with improvements in battery technology, and improvements in charger technology being offered.


cheers

Soundman you seem to be a wealth of knowledge on this subject.
And so I hope you dont mind me asking a question.
Other are welcome to answer as well!
I was given a bosch green 12 volt drill 1.5 amp hour 3 years ago for xmas
It has done bugger all work and both batteries if charged to tonight will be flat in a few days time one more so than the other.
They were never really used and so never really hit their full potential and now after charging have little capacity.
I actually set up a voltmeter and amp meter and a few globes and have been discharing them at a 2c rate a few times over the last few days. after charging they are on 13.5 volts
as soon as the load is connected they drop to 12 volts
after 5 minutes they drop to quickly to ~10 volts and five minutes after that they drop dramatically to 6 volts and so I remove them from the test rig and recharge.
I have compared my results with the sanyo cadnica 1300 mah sub c datasheet discharge chart and they fall well short of the 12 volts being maintained for the first 20 minutes then falling down.
What would be the best way to save my almost stuffed batteries?

Would popping them in the freezer and giving them a slow charge be the best way or just back in the bosch 5 amp charger be fine.
Am I to fully discharge till the terminal voltage is nigh....
Any help much appreciated....
cheers Rileyp

Rileyp, I'd like to think you could use any number of the above suggestions and even put the battery pack in the fridge, but I suspect that the long period of non-use is probably the worst possible scenario. My gut feel, and it's non-scientific gut feel, is that you are not going to be able to recover these two battery packs. Buying new Bosch packs is probably the best solution even though it's a bit costly, but it will save a lot of time and frustration.

I have to agree that they may be a lost cause...... so what have you to lose.

Stick em in the freezer, for 24 hours, then give em a hard charge on the standard charger, the run them in the drill as hard as ytpu can for als long as they will.......
givem em a few hard charge discharge cycles, you might wake um up but I dont like your chnaces.

cheers