Introduction: Cordless Drill - Improving the Battery

Picture of Cordless Drill - Improving the Battery

I hate it when my cordless drill gives up in the middle of a job. It seems that the supplied battery packs just don't cut it. So I opened up the battery pack and replaced the NiCads with much longer lasting NiMH batteries. Now I get a much longer use between charges.

Step 1: Disassemble the Battery Pack

Picture of Disassemble the Battery Pack

My battery pack had 4 Torx screws (I later replaced with regular Phillips screws for easier access). Inside you'll find 10 NiCad batteries. They appear to be just a bit smaller than 'C' cells, and all attached together in series. 1.2 volts X 10 cells = 12 volts. The cells are marked as 1300 mAH which is why they don't last very long. You will probably want to photograph the arrangement of batteries since you will need to make a new pack look just like this. Also notice the thin insulator that keeps the top battery from shorting against the batteries on the bottom.

Step 2: Assemble the New Pack of Batteries

Picture of Assemble the New Pack of Batteries

Aquire a new set of identically sized batteries. In my case the size is called 'Sub-C'. I got them at for $24.00. They come with tabs attached. Carefully assemble the new cells into the same arrangement as the original, and solder the tabs appropriately. Be careful not to short out a cell while assembling it - even briefly! You will also need to scratch the surface of the leads before soldering and put a thin coat of solder on each tab before assembly (called tinning). Re-assemble and test. Be sure to re-use the fusable link that came with the original battery pack

Step 3: Notes

Picture of Notes

Capacity:The new batteries are rated at 3000 mAH, so expect more than twice the run time than the original pack. You may wonder -- will the higher capacity hurt the tool? No: the important thing here is that the voltage is the same, but you may end up working the tool harder with the increased capacity, so don't over-do it. I've been using it for about a year and a half, and it's been excellent.

Charging: Since my old charger is expecting to charge 1300MAH NiCads, it will require a much longer charging time. The spec sheet that comes with your new batteries should help you here. Also checkout for more important detailed info on charging different types of batteries. A better charging method may increase your battery life.

Why do the batter packs die? I've been analyzing the old cells, and I've noticed that several of the cells are bad, but many of them are ok - it only takes one dud to render a battery pack useless.
Since the drill came with two battery packs, I can combine the good ones to make a second working pack. The old cells can be tested as shown below - the important part here is the load. I've used a flashlight bulb as a load which also server as a visual indicator of the battery's charge. Testing without the load will give useless results. I've seen some cells read 1.2volts without a load -- which seems good, but drop to 0.3 volts when the load is added -- clearly a dud.

Economics: A good mod should be economical too! Sears wants $40.00 for a new battery pack - if you can find it (I paid about $75 for the tool with two batteries - so why is a replacement so expensive?) So with this mod, I get a better battery for $24.00

Safety notes: Like many of the projects here on instructables, there are potential safety problems if you don't know what you are doing -- so if you don't know your series circuits from your parallel circuits STOP! don't attempt to perform this mod - it can be potentially dangerous if the cells are mis-wired or short circuited. Also beware any leaking chemicals from bad cells. Also make sure your soldering skills are sufficient before working on this project. A reader from Makezine's blog noted that one of the solder tabs is thinner than the others - this acts as a fuse - make sure you include the fuse in your completed pack.

Environmental issues: dispose used NiCad cells properly. Your new HiMh batteries are more environmentally friendly though some still recommend re-cycling.

Step 4: Soldering to a Battery

Picture of Soldering to a Battery

Update May 2011:
It's been five years since I posted this instructable - and I have another battery pack to work on. This one is a 19.2 volt pack, but still uses the Sub-C Ni-Cd batteries that my old drill used. Once again, I found that there were a few cells that were bad - making the entire battery pack useless. This time I'm just going to replace the bad cells with identical cells. The procedure is the same, but this time I decided to make a video of the soldering which can be a bit tricky.

I've already removed the bad cell from the pack - now I'm going to replace it with a good one.

Be careful not to short circuit any of the cells while soldering.

(I should have cleaned off the soldering tip better before I started)


Mag8891 made it! (author)2017-11-16

Can't see my new pack on the photo, only old battaries, but all assembled and it works! Which is quite impressing considering that I am a girl and never soldered batteries before) thank you for awesome imstractions!!

haselot (author)2017-01-09

Thank you Brian :) This is very good alternative

beautysmistress (author)2016-06-01

thanks.. great post

JamesL32 (author)2015-07-07

Lots of good info/experience here. Ultimately, the fix for a "dead" NiCad seems to be the following gradation/choices: 1) Try the voltage ZAP with a larger voltage to "melt" the crystallization. Works for awhile. 2) Disassemble, test and replace the faulty cells in the pack, either with new NiCads or NiMHDs. 3) Try to make up a new battery pack with LiIons. This means balancing the cells, finding a new way to charge them and being really careful in soldering them in series in groups. Or 4) see new DiY Instructable for an Adapter for your NiCad tool. This one is for B&D Firestorm tool 18V sliding batteries, but could be adapted (adapt the adapter?) for your Dewlt or Sears, or... to run on Ryobi batteries...

.Look for "Black and Decker Adapter for Ryobi Battery"

idrees fathuhee (author)2015-03-20

which material it have

PhilS. (author)2015-03-01

li-ions are a whole new ballgame. they have a circuit board inside that makes them a brick if they are run down to far.. I been working with some for a few days and they don't want to fix. they are DEAD and don't want to be nothing else but dead..

russ_hensel (author)2015-02-05

Just a note to let you know I have added this to the collection: Cordless-Drill-Battery-Maintenance !


Take a look at a bunch of different/similar approaches to this project.

vinniej (author)2014-04-11

Well this is a good "smack it a good one" story;

I have a multi-rotor that I crashed hard into a tree, wall, car and fence. Only my second RC flight, ever. The quad copter then would only give an error message via led's and would not work, I was devastated because I was out $600.00 + I had saved hard for--took me a year. The LED code said "call the company" RIGHT its in China and I gave up after several days of no answer and multiple attempts to decipher Cinglish instructions. After two days of internet searching I found a forum post buried on page 100K of a Google search and it said a company rep for this quad copter advised him (the forum poster) on the same problem recommending the following fix: Remove the "brain" (a DJI NAZA V-2 in this case) and hold it in your right hand about 7" above a ceramic counter top with the writing on top, then rap it moderately hard on the counter top .

I was reluctant but desperate so I tried it. To my total amazement it not only fixed it but it flew better than ever after this "smack it a good one" fix.

dodgeramman (author)2014-03-01

I'm a bit skeptical but there is an easier way than doing this and doesn't cost anything . batteries built up with crystal like particles (best way I can explain it ) that makes your NiCad batteries lose capacity over time . I've come across a way try and zap them with a battery charger without taking them apart or buying new batteries . I zapped a couple batteries I've had since buying a 4 piece set in the 1990's 18 volt Dewalt .Checking now to see how long it will last just in a dewalt radio . Will post results later as I'm experimenting now .

ironsmiter (author)2012-02-03

Almost 6 years later, and still good information.

The one thing I took away from this, that i will be grateful for as long as I can remember, is the Soldering Video. That little trick/tip is going into the printed long-term storage

MTtoo (author)ironsmiter2012-02-08

Ironsmiter, I need to pick your brain a bit. I have a stack, probably a couple dozen, batteries of various makes that I have "liberated" from a big box stores recycling box. One at a time naturally!! Most are 18 volts. My 18 volt charger is dead. Now to the question.....Would it be possible to use a 120 AC transformer that puts out 24 volts AC? Read on before you shoot me down. Put a bridge rectifier on the output to convert the AC voltage to DC.
The new transformer is a Honeywell 120/208/240V, 60 cy, primary to 24 VAC 40VA secondary. I am sure the 40 VA would take some time to charge a 18 volt drill motor battery. All of the instructavles I have read deal strictly with batteries. None mentions the care and feeding of the chargers. Care to share any helpful hints?
I am not a professional so I needed someone with brains to clarify my idea.

ironsmiter (author)MTtoo2012-02-08

wow, wow WOW... overkill.

Unless you're putting dozens of those cells in parrallel, 40VA is gonna DESTROY them.

I'll give you a summery of my research and calculations, as best I can.

Bear in mind, my power supply is going to be a 30 volt HP printer power-brick.
That brought my current limiting resistor VERY low ohmage, and wattage. 10 Ohm, and 1/4 watt.

Now, since you're starting with 40 volt...

The charging voltage is going to be approximately 1.4 v per cell.
You have what, 15 cells? (15 x 1.2 vdc nominal = 18 vdc)
So you need 1.4 x 15 = 21 vdc to charge.
24 v (supply voltage) - 21 vdc = 3 vdc voltage drop across the resistor.
Your cells are probably 2.5 Ahr. You need to charge C/10 , or 0.25amps.
R = E/I = 3 v / 0.25 = 12 ohms.
3 v / 12 ohms = 0.25 A
3 v x .25 A = 0.75 watts
I would upgrade to a 1w or eve a 10w resistor. they're only a dollar, and the added safety is worth it, imho.

You'll have to check VERY carefully. but if all the packs are NiCd, then 12-14 hours with the charger, and resistor described should give you a full charge. It should also be safe if you forget and leave it on a little too long. NiCd can survive almost indefinite charging at 1/10C rate. The extra energy gets converted to heat, and exits the battery through the cell wall.
Bear in mind, quick chargers like my original, have very sophisticated circuitry... but mine charged at almost 1C. it did shut off after that though, as a safety feature. Charge at 1C for 10 hours, and you better have the fire-department on speed-dial, cause around hour 3, it's gonna go Fwoosch!

Consider some googleing on "homemade NiCd chargers.
Tons of info is to be had at RC groups. they use packs much like these to fly their planes(though they're starting to switch over to li-po and li-fe)

Doh, just forgot.. you'll have to measure the ACTUAL voltage, under load, because you're gonna get a voltage drop over the rectifier. You're going to have to recalculate using the lower, measured voltage.

MTtoo (author)ironsmiter2012-02-09

Ironsmiter, you must be an electronics engineer!!
I certainly appreciate your rapid reply.
I am not that much into electronics, and had to re-read your reply several times to boil it down to my level. I am more mechanical and my dabbling into electronics is fixing things broken. Determine what is bad, cut out the old and replace it with a like item. Your reply was a real insight in how to determine (calculate) the needed resistor.

An amazing bit of info can be had on these new-fangled gadgets (computers) if a person knows where to look for it. I wish computers had been available when I was young. I pre-date Television!!
Correct me if I am wrong, but this is what I determined from your reply.

18 volt batteries have 15 1.2 volt cells.
To charge these cells will require 21 volts @ .25 Amps for 12 to 14 hours for a full charge.
To drop the 24 volt output from the transformer, after it has gone thru the rectifier, will require a 12 ohm 1 watt (or better yet a 10 watt) resistor.
Now if I can just figure out the 40VA output of the transformer...Many years ago I have read how the VA is calculated, but it escapes me now.

I REALLY appreciate your thorough explanation of my question.

ironsmiter (author)MTtoo2012-02-09

Nope! I started the same way you did.

Just happens, I post-date color TV.
Though i do remember, vividly, when the Internet switched and we all started using the WOrldWideWeb.
When I started, we Gophered instead of Googled.

If, and that's a pretty big IF, i got my numbers right then...
12 ohm, 1Watt(or higher) resistor should take your power supply, and turn it into a very crude 1/10C "slow charger" for your 18V battery packs.

Pardon me while I plagiarize.
The only difference between W and VA is the power factor. The power factor, unless known, is an approximation. For purposes of our calculations, we use a power factor of .85. The VA value is always higher than the value for W.


ironsmiter (author)ironsmiter2012-02-09

oh, and to be VERY CLEAR for the folks trolling in the background, or in the years to come...

that's AFTER the transformer is rectified.

I actually have absolutely NO idea what'd happen if you fed the unrectified AC into the battery(though I have a pretty good guess, and it involves letting out a lot of magic smoke. You know, the stuff that makes electronics work until you let it out?)

Dr.Bill (author)ironsmiter2013-02-18

The un-rectified AC would just blow the wiskers off and the NiCad would work good again. Just have to limit the AC time to a few seconds...

bclamore (author)2012-05-27

The Dremel tool effectively removes the surface oxidation. I suspect this is why the solder sticks. You could probably do just as well with alcohol and some flux. A rougher surface should also help prevent the solder site from being flaked-off. Dremel tool looks like an easy solution too.

endadmcc (author)2012-05-02

Hi i have been reading this interesting section and wondered is it possible to do the same with Li-ion batterys as i have a 21.6v with 2 battery packs and none work . When placed in the charger or drill they put the overheating light on. Anyone think this can be fixed.

mygiveaway (author)2012-03-06

I'm a newbie on here.... Need a little help is poss
I've taken apart my Makita 18v Cordless drill 2.6ah NiMH battery because it would not charge (flashing red and green). I've tested all the cells and they all read 1.34v so i'm thinking its one of the three components that is stopping the battery from charging (see image). It was hard work getting the cells out of the case and i think this may be an indication that the battery may have been over heated at some point. The charger is working fine with my other battery although that battery is also starting to loose power quickly.

Does anyone know what each of these components do and how I can replace \ bypass one or all three to get the battery to charge again?
Info: the red component was glued to the top of one of the other cells in the pack.

mygiveaway (author)mygiveaway2012-03-25

I was told that the;

rectangular Klixon component is just a fuse,

The red component is a thermal cut-out\reducer switch used for reducing the power input when on the charger if overheating occurs,

The yellow component is a thermal cut-out\reducer switch used for reducing the power output when on the battery is in the drill but overheating occurs due to heavy usage.

All components worked on this battery, so i guess the batteries can no longer hold a charge.

Hope this info helps some one.

budrootbeer (author)2012-02-11

Does someone make and sell a converter to actually plug in your 19.2 sears cordless drill and saws? Sometimes at home you don't always need to be cordless.

Dr.Bill (author)budrootbeer2012-03-21

I removed the battery from my drill motor and just connected a wire to each terminal with clips that fit and plugged the other end into my 25 amp switching power supply and it works good. lotsa power.

mymatemark (author)2012-03-02

Ni-Cad & Nimh are good at certain price points but in the long term the best battery performance comes from Lithium or Li-ion as they last longer, do not have a memory, they are lighter & provide more power right through to the last bit of use. Lithium or Li-ion batteries have no memory so when you stop using the power tool & you go to use it again in a few months the battery has the same level of power as previous. Another good thing is they do not react to extreme heat & cold the way Ni-Cad or Ni-MH does.

No need to warm batteries up anymore with Li-ion

instructableken (author)2012-02-29

I don't know if anyone actually mentioned the size name of the batteries used for power tools. It is "Sub C". I buy tem on eBay and always buy NiMH. Many of my older tools are NiCad and the NiMH gives you more power and life.

jamesjghome (author)2012-02-24

I just joined this site by happenstance.

I thought I was the only Mcgiver left but I see not. When I was a child, my Dad and mom called me “screwdriver fingers” due to the fact that I had to tear something open and see how it worked; even though not broken I just could not resist

I did the battery thing about tens years ago when I discovered the “C” batterers matched my flashlight. Aside from all the data and info in above links, if you can imagine and interpolate you can do this in about most everything

Thank God, Men are still men

MACSWAG (author)2012-02-01

Thank you so much for the very helpful post,I've just thumped one of my Draper 18v.bats on the deck and it is now charging,well the charger light is bright so I'll test in the morning,the other one same procedure the charger light comes on but quite dim , any more suggestions please or how to check which cells are duff would be helpful ,I'm in the U.K. so don't have the same suppliers as you chaps across the sea,


ironsmiter (author)MACSWAG2012-02-03

and forgot to mention...

Take your two packs, and rebuild one good one out of them.

With the now empty battery case, rebuild it will ALL fresh cells.
That should get you the best bang for your buck/euro/pound.
Keep any extra good cells for when, not if, WHEN, your newly repaired pack
kills another of it's cells. When you run out of THOSE spare cells... recycle all the old cells, and rebuild with new tabbed cells for what is now the third lease on life for that battery pack :-)

Now, we're 10-15 years into the future of your tool, and it's probably worn out. Time for a new cold-fusion powered drill.

ironsmiter (author)MACSWAG2012-02-03

You don't need the same suppliers, for checking which cell is bad, just any old cheap volt/ohm meter.
As for buying the new tabbed battery cells... don't we all buy them from the same Chinese manufacturers?

Check the image in step three.
If the battery is freshly charged, that "light bulb load" is pretty important.
It helps bleed off the "surface charge" on the cells, and gives you a "working voltage" to measure.
Test the cell voltage after 2-3 min of running the light.

If you're "lucky" like I am...
I ran my batteries in a sawsall, till it quit sawing.
hen took apart the packs that weren't performing(one lasted less than 3 min of sawing)
When i took apart my Bosch 24V pack, most of the cells tested fine with the volt meter.
FIVE of them tested ZERO volts.
Guess which cells were bad? ;-)
This only really works if its a few bad cells, and you run the battery to "dead".
The down side is, if a cell is only starting to die, this may not catch it.

eel_dahc (author)2012-01-12

I just redid one of my Craftsman 19.2 batteries. What I did was a little bit different. I bought an 18v battery pack from Harbor Frght (HF). It was a gamble really because I didn't know for sure how the batteries were arranged in the pack. Luckily they are arranged in the same shape, however they are connected differently. Luckily though there are wires already soldered and coming off of the pack that are long enough to make it work. My original craftsman pack had various bad cells. But, the cell connected to the terminals(the one on the top of the pack) was still in great shape. So, I snipped the nickel strip off the bottom( leave as much as you can though so when you solder you can hold the strip with pliers to sink the heat ) side of the top battery and the negative wire going to the rest of the pack. I then carefully pulled out the fuse/resistor wires making sure not to damage them. Then I soldered the red wire coming from the HF battery to the bottom of the cell with the terminals on it and the black wire from the HF pack to the black wire going to the cell with the terminals I then tucked it all into the craftsman battery case, put the top on, screwed it back and then charged it up. Perfect. If you do this make sure the battery with the terminals is still good. If it is not then you will have to replace that cell with a new one. Best of all, the pack cost $10, on sale for $12.99 with a 20% coupon.

gsnoorky (author)2012-01-04

That pic looks like my 12V Sears Companion drill battery--I'm working on that now. It doesn't seem to work very long in the drill--a few secs, and it slows. I did do the battery starter trick--it was at ~10V--now, it's at 13+ V. I rapped it on the floor a few times and put it back on the charger--instructions say to leave it on for several hrs.--maybe even six.

I'm also working on my two Milwaukee 18V "Power-Plus" batts. Using the same trick, one seems now to be the usable battery for the drill I had loved--the drill turns solidly again! The other batt may be too far gone. It did go from 0V to ~3.2V, though. The charger doesn't accept it yet. I'm nowhere near ending the fight for it: I'll cut it open and go NiMH, if necessary.

Big box HW stores want $70-$80+ for such Milwaukee 18V batteries: Well, I then knew that the expensive drill screw wished to turn into myself! Amazon was somewhat more reasonable: $50+, yet, I haven't checked lately. Thus, I haven't used my originally priced $200+ drill for a couple of years. I was about to give up and purchase Skil or B&D--or even cheapo HFT or Big Lots!

(These Milwaukee batteries don't use the familiar vertical post most drill batts often use. Three side-shielded terminals "slide" horizontally into the drill bottom or the charger. As for checking such unmarked terminals for polarity, use a voltmeter to find the terminals which give a positive voltage reading--perhaps after charging. For this Milwaukee 18V "Power Plus" ni-cad battery, apparently the terminal on the far left (terminal side up and terminals facing you) is neg (-)--the one directly next to it, on the right, is the positive terminal (+).)

Thanks for the great inputs here!

cjq (author)2011-12-09

Hi folks, I've read comments about re building 19.2 Craftsman packs, I still have a problem. I bought 6,000 mah batts with tabs . The pack is complete and has been charged . I had difficulty getting the charging to start. I found the "old" battery pack corroded real bad. There is a tiny circuit component ,a thermo device I think . I had to by pass thin device . I also found a "fuse" link ? I think it is ,and that was broken,I by passed that also. Now here's my concern,,the charger has a red lamp to indicate charging and a green for full charge. Upon initial incertion the green lamp lighted . I know the new batteries needed charging but the red lamp did NOT light. I left the pack on charge overnight and the batts have charged to 21.5 volts surface charge . After a little use the voltage dropped to 20.5 . How do I correct my charging difficulty. The battery pack had NO temperature rise overnight. I'm thinking the Batteries were in a trickle charge,,,make sence? I need some technical help Thank You


bricabracwizard (author)cjq2011-12-31

I think if you want lots of answers post this question to the forum, hopefully you'll get an answer soon, sorry I don't know the answer.

dcobrien2000 (author)2008-10-07

I have a set of 18V Coleman tools that came with 2 batteries. A while ago one became hard to charge and finally the other failed. I could not find replacements anywhere so I was faced with buying new tools (lots of $$). I found this post and then the link about reviving rechargeable batteries, it said that crystals can build up in the batteries and short them out. As a fix it suggested hitting them with a blunt object. I opened up the batteries like this post suggests and then whacked the cluster of batteries firmly with a rubber mallet. To my surprise it worked, they now hold a charge and work great, no new tools!

I wonder if that physical shock breaks the crystals like electrically shocking does. Anyone try this with an unprotected Li-ON cell?

snet (author)dcobrien20002011-11-12

I recently ran a cross a Makita 6343D with 2 18v NI_CD batteries and a charger on one of the free auction sites. When I received the drill one of the batteries worked fine but the other wouldn't work at all, even though the charger showed it "charging".

I wasn't too concerned since this whole lot was FREE but after reading this I simply tried cleaning the metal contacts with rubbing alcohol and lightly wacking the bottom of the battery with the rubber handle of a hammer and POOF it started working again and holds a charge.

Thanks again for the great advice! =)

fromjim (author)dcobrien20002010-10-26

I was about to trash a good Craftsman cordless drill because the batteries would not accept a charge, I was in the process of trying to find good replacement batteries at a reasonable price when I came upon this site, I tried the above tactic, whacking the battery pack hard several times on a block of hard wood, I then placed it in the charger and it began to charge, an hour later I had a fully charged battery, even the weak battery that would take a small charge benifited from this procedure.

Thanks a lot guys,

God bless


crazyg (author)dcobrien20002010-08-03

i will try that:-)

wupme (author)dcobrien20002009-08-25

Its always surprising how many technical stuff you can fix with whacking it. A wack actually fixed my digital preamp on wich an amp technican gave up... Its also a cool way to fix something.

-max- (author)wupme2010-07-18

LOL! i once fixed a camera with "lens error" by trowing it at a wall!

jeff-o (author)dcobrien20002009-08-18

I'm delighted when the fix for a problem is "hit it with a hammer." :D

chenxinghao (author)2009-06-12

I have two bad Craftsman 19.2 volts EX batteries that when pluging in to the charger it will go GREEN and no charging to take place. The bolts seem to be the HEX type but my HAX drive could not go in. I noticed that there is a little round/dot in the HEX openning that is preventing the tool getting in. What type to tools to use to unscrew the bolts?

I've seen those, they suck. I'd do a search for special security bits.

But in a pinch.

bgentle (author)chenxinghao2010-04-15

It is a security screw that uses a torx screwdriver with a hole in the center. Take a punch and punch the round dot as you call it out or use a dremel too to grind it out then use a torx screw driver to remove the screw.

Hubiewan (author)chenxinghao2010-03-12

Hi:  I have broken off the little pin inside the security screw, allowing your regular torx bit to work.  I do reccomend purchasing the security bit set from Harbor Freight.  On of them is cheap enough and quite extensive.  Hubiewan

nukemmcssret (author)chenxinghao2009-08-25

Get a drill bit a little bit smaller that the head of the screw and drill out the stripped screws. The head should come off both screws. remove the cover and there should be some of the screw exposed. You then grab it with a pair of needle nose and turn out the screw.

Caspar (author)nukemmcssret2009-10-15

Before the pliers bit, heat the screw head with a soldering iron tosoften the plastic.

achollowell (author)chenxinghao2009-10-01

that is a security bolt I have see this type of bit at harbor freight

I find with my charger when it does that is to put the battery in the charger then unplug it and after a few seconds plug it back in. Hope this works for you.

They are security screws or torques. Check with you hardware supplier for a set of driver tips

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