Thread: Cordless tool batteries

Unfortunately, I would have to remove some beer from my fridge to be able to do this! )

I guess it really depends how cold your fridge is set - the batteries on my tools get rather warm when charging and it being about 25° at the moment would not really help.

Does he also make sure they are *really* flat before re-charging - I've heard this also helps with the life ...

Yes I’d have a similar problem with the fridge and getting SWMBO to sanction a workshop fridge isn’t very likely.

I asked if he ran em out flat but no he doesn’t "just flat enough so that they won’t do the job at hand anymore".

The battery in the fridge is a new idea to me....

I have 11 yr old makita 7.2v with 2 batteries - still original and still holding charge as well as they used to - the unit has gotten a regular flogging over its lifespan. I do make sure the batteries are completely flat by wedging the drill in a vice to completely power down before recharging. I've been told this is the correct thing to do....

If I remember correctly from my tech days nicads take longer to accept a charge at lower temps also are slower to release the charge whilst cold too.

I think you'd only get condensation if you whacked them in the fridge to charge 'em whilst they are still hot.

A friend of mine used to race RC cars, to avoid battery pit stops it is common practice to charge the batteries in an esky, this allows more charge in to the battery (as heat interfers with the charging) and hence it lasts longer before going flat. There was no indication that the battery its self would last longer. If you need to know about charging batteries talk to the local RC club / race track /shop

Disclaimer this is all second hand info that I didn't understand at the time. Any impression that I know what I'm talking about is unintended. Any similarity between this and good advice is purely coincidental.

Don't know the science behind it but I find when using my 12v cordless all day and constantly recharging the batteries, they gradually take less and less of a charge and so go flat quicker as the day goes on. So I stick one in the freezer for awhile and then put it in the charger and it seems to take a longer charge.

Apparently when yo use a rechargeable battery it leave miniscule sections of bad 'memory' on the battery. When you charge it those bad spots will not take a charge. The more you use the more bad sections there are. Putting the battery in the freezer erases the memory and you're good as new (almost). I'm no expert, this is as it was related to me by a RC Car racer.

Dan

I have had some good luck on an old laptop freezing dead batteries for a few days (wrapped up protectively in plastic), then recharging them. They did come back to life.

Recently I repacked batteries in a relatively new - 2 year old -Panasonic drill (15.6 v) and was told that the Metal batteries, while able to create a higher level of power, were much poorer at holding this over time. The recommendation was to repack with the older technology (?), which I did. The drill works very well again. I also have another, much older Panasonic drill (12v) with the old style batteries, and these have lasted 7 years so far without missing a beat.

The moral of the story is that new technology is not necessary better.

Regards from Perth

Derek

Where do you get the new cells from and do you save much on the cost of just buying new ones? I think my 5 year old 12v batteries are getting near the end

Many of the general battery shops (such as Batteries for every thing) will repack your old cells. An 18volt cost me $89 a few weeks ago its depends on the voltage though.

I have repacked many batteries over the years, and they generally do seem to last longer than the originals (I seem to be very hard on rechargeable though).

Apparently the art in repacking is that they closely match the individual cells, they tell me that even on the more expensive tools the cells are not matched, this means a reduced life due to the lower spec cells grabbing power from the higher spec cells causing extra heat etc.

Heaven knows if all that’s true but that’s the gist of what I was told.

Hi everyone,

I have a ryobi 6.5mm 7.2 volt drill which has been in use constantly IE: at least weekly and is now 22 years old. I always
charge when completely flat, do not use any cooling systems and the thing still performs as good as the day it was given to me as a gift for fathers day. This drill has never been opened up for any reason and has original battery. The most remarkable bit of gear I have ever owned.

This item was assembled in Taiwan.

I bet not too many of the newer pieces of gear do as well !!!


Kind regards

Mike.

I have a 7.s volt ryobi cordless. drill, dunno how old, but I seem to remember my great granpappy inheriting it. When the batteries died and no longer took a charge, I added a cord a couple of alligator clips and a hook it to a convenient 12V battery. Yeh Yeh I know, it aint' no longer cordless. But it is semi portable to places where there ain't 240. It has the more torque and drives screws/drills quicker thatn ever, and it gonna burn out quick too, but I'm still getting some use out of it.

I pulled one Nicad pack apart and found a bimetal device mounted in the centre, this activated at a certain temperature and caused an interuption to the supply and electronically turned the charger off.
Does this shoot the other claims down in flames or is this just another sort of device.
The batteries were in a thermal clad device (a thick cardboard tube) so it took a while for the device to become warm from battery heat.
The miracles of modern science.

We don't seem to be getting any responses from those that really know all about these things - there must be somebody out there!!
I will add my little bit
Fully discharging NiCads EVERY time before charging and fully discharging NiMH about 1 in every 10 chargings does make them last longer. There are many complex chemical reasons for this and they are all way above my head.
One problem with this is that in a pack there are many individual cells. The number of cells equals the pack voltage divided by 1.2, 1.2 being the voltage of the individual cells. No matter how well matched the cells are, you are not going to fully discharge all of them at the same time. The danger is that one cell will discharge first and will actually be charged IN REVERSE by the remaining cells. Once this has happened the pack will rapidly deteriorate. Lower voltage packs, with fewer cells, actually are less likely to have this happen. With a high voltage pack, say 18 volts with 15 cells, one flat cell may not stop you using it.
It is best to run them flat UNDER LOAD. With a drill running free it is easy to over discharge them.
Heat and cold - they are damaged by heating, particularly when they are being charged. Many packs have a heat sensing switch in them to stop the charge if they overheat. Some charging devices use the pack temperature to stop the charge.
How long a pack lasts depends on your skill in looking after it and luck - how well matched were the cells.
I also have a Makita 7.2volt drill - mine is 18 years old and it is only into its 2nd pack.
Cheers

...and were too afraid to ask? This is probably going to be way way too much info, but here we go...please feel free to stop me at any time.

I used to race electric RC cars, and still have all my NICAD packs, about a dozen or so, so I may qualify to answer your questions.

Please Note: I said 'used to race'...therefore I'm not disqualifying myself by association after you read the next paragraph )

Generally speaking people who race electric RC cars are NOT the best people to give you advice on the correct handling of Nicad battery packs, especially if you'd like long life out of them. They are interested in one thing only... and that is winning. This means cramming as much charge into your pack as possible, and getting it out as quick as possible. Please keep in mind RC races only last 4-5 minutes, and if you have charge left in the pack at the end, you didn't gear the car properly!

Car Racing packs are 7.2v (6 cells). When I raced, the really good packs were imported from the US and Japan and very expensive ($200+). As mentioned in an earlier post, they are constructed with 'matched cells' so that the internal resistance of all the cells was both very low and the same for all cells (or at least very close), as the current drawn out of the pack is limited to the current supplied from the cell with the highest internal resistance (the cells being in series).

The packs were also 'zapped', a proprietary process where (and we're going back a couple of years, so forgive me if the details are sketchy) high-voltage pulses are forced into the packs to change the chemical structure of the electrolyte and lower the internal resistance. This 'zapping' is also known by other names to other manufacturers, but alas the names escape me. Packs are also deep-cycled (charged/discharged/charged/discharged over and over) to condition the cells to give maximum output.

Nicads have strange charging characteristics. The voltage of a cell/pack gradually rises over time as it's charged. As the pack reaches full charge, the voltage peaks, then drops slightly. At this point the cells heat up significantly. Peak-detect chargers are designed to sense this voltage peak, and cut off at exactly this time. El-cheapo RC car pack chargers, and those that come with bargain-basement power tools, do NOT use this method, they are either a set-time charge, a slow trickle charge through a piece of resistive wire, or a manual charger which you stop when the cells get warm.

These methods are extremely random in their effectiveness, mainly because no two packs are alike, and for them to work the same way every time, the pack always needs to be in the same state of discharge when charging starts. My Metabo Cordless has a peak-detect charger, so I gather it's only the bargain end of the market that suffers.

Normally you would charge your 1700-2000 mAh pack at around 5 to 10 Amps using a peak-detect charger. Racing motors, even though they are only 50-odd millimeters long and weigh a couple of hundred grams can draw in excess of 30 Amps for five minutes. Professional Racers in the US charge their packs at >25 A, the reasoning being 'what goes in comes out the same way'. They get one run and one run only, out of their packs, but it's a good one. Then they throw the packs away. They're normally sponsored by a battery manufacturer so they can get away with this without going broke. I was very conservative, I used to charge all my packs at 5A the night before the race meet (it took about 25 minutes per pack). Overnight the cells cooled, and just before a race heat I'd 'repeak' the cells to make sure they were ‘full’.

Nicads also have strange discharge characteristics. Contrary to popular belief, you should NOT (and I emphasise NOT) discharge your packs completely to zero volts. If you do so, it has a few ramifications:
* The cells can spontaneously change polarity (i.e. the cell negative becomes positive and vice versa). This is probably why a lot of people suffer premature pack failure. One or two cells in a large multi-cell power tool pack can significantly reduce the voltage and current available.
* When you try to purposely flatten a pack by using excessive current, the heat buildup can and will damage the cell structure.

Ideally you should discharge a pack so that each cell reaches a discharged voltage of 0.9 Volt. For a six cell 7.2 V racing pack, the cutoff point for discharge is therefore 6 x 0.9v = 5.4 volt. At this point, even though the cell is at 75% of its nominal fully-charged open-circuit voltage of 1.2v, the current available is only about 5-10% of the total cell capacity. This point is as low as you can go without running the risk of reverse polarity occurring. Packs should also be stored discharged, not charged ready for use.

After the races finished I used to discharge my packs to their storage voltage. I modified a Dick Smith kit and designed a auto-discharge circuit which was self-powered and used a bank of 12 volt taillight bulbs as the load. A 6 volt VW headlight relay was used to do the switching, as it would hold closed down to 5.4v, then the whole thing used to switch itself off. I use this sort of thing on my Drill packs as well now and again. You don't need to go to this extreme, a mulitmeter and a watchful eye can achieve the same thing.

Nicad packs also have the tendency to develop a 'memory' effect. This occurs when the packs are only discharged to a point where they are still holding substantial charge, and then recharged to full capacity. Eventually chemical changes within the cell electrolyte will occur and the pack will only discharge down to this point and no further. This is also a major reason packs fail prematurely. There are companies who specialize in reconditioning battery packs, they use a deep-cycle method, although not having used one I’m not sure what the long-term prognosis is...

I’ll stop now, I'm getting tired. Let me know if you'd like any more info!!!

Hope this helps.

Relevant websites:
http://www.modelflight.com.au/rc_mod..._batteries.htm
http://www.copquest.com/battery_care.htm

Mick