View Full Version : cordless drill batteries

12-01-2005, 11:40 PM
Both my fatherinlaw and I have the same dewalt drill, it's the 18 volt version. Well, we have five batteries between us, but three of them will not hold a charge.

Someone on one of the lists suggested very quickly jumping 120 volts across the terminals. The theory is that between the plates inside the battery, small conductive crystals form. They go from one plate to the other, thus shorting the battery out and draining it. By hooking 120 volts to it very quickly, you are burning the crystals.

NOW. I'm not an idiot, I'm not going to place the batteries on my naked body and plug this in like this...I'll probably put it in a 5 gallon bucket to try it...just in case something bad were to happen.

Before I do this and post the results, who thinks its gonna work and who thinks it's gonna explode (or just not do a damn thing)?


J Tiers
12-02-2005, 12:24 AM
Sheesh....... 120V?

I don't think so............

What I HAVE done, and had it work OK, was to take an INDIVIDUAL cell and "zap" it on a 6V car/traction battery....

Connect one wire between batteries, and just brushing the second wire on the terminal, not "connecting" it. "-" to "-" is how I did it.

You have to find tha bad cell to do that, you don't want to zap the good ones along with.

Fixed it for a little while, but it always comes back again.

12-02-2005, 12:49 AM
the other problem is 120 is AC and the 18 v is DC, I dont know for sure what would happen but I dont think the results would be favorable

12-02-2005, 01:07 AM
Hmm, that's interesting. If the cell was shorted, and one was to assume that a short on the 120 vac line was to pass say, several tens of amps until the breaker blew, then it probably would be safe to say that the short would get burned out. Until the breaker blew, you'd have a very high pulse charge for .017 seconds, then a pulse discharge for the same time span, cycle repeating. In other words, no net charge or discharge. That in itself might save the cell's chemistry, but if any gassing was to be generated, it probably would be at a high rate of speed. What gas is that, hydrogen? Burning the shorts out would presumably create a mini fireball at each point. A memorable event could follow http://bbs.homeshopmachinist.net//smile.gif

But I'm all for hooking up those Defalt batteries to line power.

[This message has been edited by darryl (edited 12-02-2005).]

12-02-2005, 01:52 AM
One fault which occurs with Ni-Cads is the formation of "dendrites", crystalline structures which can short-out the cell.

It sounds like the "120V" trick is intended to blow the dendrites away.

I would certainly not do this; it is dangerous, even with 120V (we have 240V in Australia).

The standard "cure" for dendrites is to charge-up a large capacitor, say 100 000 mfd or more, to its rated voltage, perhaps up to 63 volts. There is a LOT of energy stored in a capacitor of this size.

Connect the capacitor across the battery and this energy is discharged in a few milliseconds; the theory is that it will blow the dendrites away.

Sadly, it doesn't always work. It can work when applied to individual cells but a drill battery is a set of cells in series; one "dud" can pull the whole battery down.

It is often possible to dismantle the battery pack and replace the cells but you will usually find that it's cheaper to buy a new "non-genuine" pack.

There are some good ebay stores that offer battery packs for drills etc at a reasonable price.

12-02-2005, 02:06 AM
The capacitor trick can work sometimes on individual cells but not usually on a pack. DON'T use 120! I wait for the same model of drill to go on sale around here and can pick up another drill with two packs and a charger for less than the price of a replacement battery.

I gotta figure out something to use those drill motors for. A small robot seems like a possibility. Of course, you can easily add a cord to a drill to run it off the cigarette lighter plug on a vehicle or a portable power pack. Still easier than running an extension cord out into the yard or something.

12-02-2005, 02:17 AM

Good idea re abandoning the battery and running the drill from a power supply. I have a little old Makita hand drill to which I did just that; it's useful in my electronics workshop when I just want to put a quick small hole in something without going downstairs where the big toys live.

I think it was originally about 4V8; it runs nicely from a 12V supply. It draws a lot of initial current, though.

12-02-2005, 08:34 AM

[This message has been edited by JPR (edited 12-02-2005).]

J Tiers
12-02-2005, 09:18 AM

One problem with that, which is bad....

If you run it 'dead", you risk reverse-charging any cells with lower than average capacity. There are always some.

That seems to make them go bad faster...

Best plan is to recharge the pack as soon as you detect a loss of power.

That point is when the cells have "turned the corner" and are rapidly dropping in voltage. Somewhere on that down-slope, the slightly lower cells will "run dry" and begin to reverse charge.

12-02-2005, 07:43 PM
<font face="Verdana, Arial" size="2">Of course, you can easily add a cord to a drill to run it off the cigarette lighter plug on a vehicle or a portable power pack.</font>

I've done exactly that Evan. I drilled all my gate posts with it.

When my drill batteries went belly up, I located a supplier online but never ordered any. As I recall, the "Sub-C" size were about $1.30 when purchased in quantities of 10. Sure beats Rat Shack's price of near $4 each.

12-02-2005, 09:55 PM
Had an old 12v drill that the batts when dead on, had them rebuilt by a place like radio-shack, can't remember the name though, anyway they charged about $20 for each battery but they rebuilt it with a 75%greater watt-hour rating. Thier life span is supposed to be greater than the brand-name replacement batts.

12-02-2005, 10:25 PM
What I don't understand is why the hell DeWalt still uses NiCad batteries in this day and age - NiMH are relatively cheap and give much better performance, both in output and battery life.

They don't suffer "battery memory" either.


This Old Shed (http://thisoldshed.tripod.com)

12-02-2005, 10:31 PM
Well as far as model airplanes go now, the electric variety, eveyrone is using Lithium Ion and brushless motors. Just dont draw too many amps from that lithium battery!
Only good thing Nicad has going for it is its ability to discharge at higher amps. Having been in the hobby for many years I dont want to touch another Nicad or Nimh for ANYTHING!

12-03-2005, 12:04 AM
BillH, what's the deal with lithium ion batteries for r/c- how come nicads which used to be the ultimate battery for r/c use are now not worth having? You say watch the amp draw from lithium ion, that almost implies that they have to be babied like nicads, just in a different way. Is the higher power/weight ratio the major factor in using LI? I just want to hear the scoop from someone who has hands-on experience with the newer battery types.

J Tiers
12-03-2005, 12:23 AM
<font face="Verdana, Arial" size="2">Originally posted by HTRN:
What I don't understand is why the hell DeWalt still uses NiCad batteries in this day and age - NiMH are relatively cheap and give much better performance, both in output and battery life.

They don't suffer "battery memory" either.


They seem to have a similar effect.....

When my laptop has not been used for a while, the batteries will not recharge correctly for two or three charge-discharge cycles.... They are NimH type.

Probably not the exact same effect.

But you can sure tell the difference between 20 mins and 1 hour before the low battery warning goes off.... The 20 mins is the first charge after not using it for a while. The 1 hour is normal, usually achieved on about the 4th or 5th charge/discharge cycle.

I understand they do not have a dendrite problem.

12-03-2005, 06:32 PM
I'm kind of wondering how the voltage cutoff circuits in digital cameras, etc, are interfering with battery life. It's entirely possible that nowhere near the full charge is used before the camera shuts off. Of course, the batteries are 'dead', so you recharge them. But maybe you're only getting two thirds of the charge before the camera decides that they're 'dead'. Then the charger shortens their life by overcharging them each time (because they aren't really dead, just down by two thirds) I know that there isn't a very large voltage window between full charge and low, because I can't even measure the current draw on my camera's batteries without the camera shutting down. I'm not losing that much voltage through my current measuring meter, but it seems the small amount I do lose is enough for the camera to sense a low battery.

A cordless drill doesn't usually have a cutoff circuit, (though my bosch does) so it's free to use all the charge, at least until the first cell goes dead. I think we are being saddled with poor chargers.

Bruce Griffing
12-04-2005, 04:25 PM
Here is a link on replacing bad cells.


Many internet suppliers offer replacement cells - just google "sub c cell" and you will find lots. Recently, Home Depot had two 18v Ryobi batteries on sale for $39. I was not interested in Ryobi, but I did think it would be a very cheap way to get 30 replacement sub c cells.