Introduction: Hot Rodding a Power Drill Battery

Picture of Hot Rodding a Power Drill Battery

So, your power drill battery dies. What now? Fork over 85 bucks for a new one? I don't think so. After searching high and low on the internet for a good price for a replacment battery I found the retail for my Black & Decker 14.4V to range from 35-85 dollars. Riiiight. Time to make your own!

At this point it would be good to mention you should really discharge the pack before you continue. Don't play with electricity unless you know what you are doing!

Step 1: Let's Find Out What Is Inside!

Picture of Let's Find Out What Is Inside!

I had a little brainstorm and decided to open this thing up and see what makes it tick. It's funny, I always thought there would be some mystical magical component of power tool batteries that justified the outrageous know, custom made or ethereal glowing lights or little elves or something. Turns out they are just a rip off.

Fortunately for me the internals were looking familiar, a simple set of "Sub C" rechargable NiCd cells from my RC car racing days. I used to build my own racing battery packs so I couldn't help applying that here.

I had visions of using batteries that power world championship RC cars and transform my moderately powered B&D; into a drill that would make screws and yet-to-be-drilled holes tremble with unspeakable fear.

When you open the battery you'll need to save some plastic bits detailed below. Don't break them.

Step 2: Replacement Sub C Cells

Picture of Replacement Sub C Cells

At this point I came back to reality. The racing batteries alone would cost a hundred bucks. So, I settled on a brand name NiCd cell from GP. The main difference from the stock batteries is that these are 2000 mAh cells and the stock ones are only 1700 I should get more run time...basically a bigger gas tank.

These fellas cost me $1.79 each for a grand total of $21.48 from Budget Batteries. So far so good.

In case you aren't good at math, a 14.4 battery takes 12 1.2V cells to make up a pack.

Step 3: Battery Bars

Picture of Battery Bars

Next up on the bill of materials are some RC parts. These 24k gold plated battery bars are from Novak racing. I couldn't skimp everywhere. A bag of 28 was about $14.00 from Tower Hobbies.

I only needed 10 to assemble one pack, but I have another drill battery waiting do die. So, that's five bucks for the bars and up to $26.48 total. Still ten bucks shy of the best retail price I could find ($35.00) Incidentally that price was direct from Black & Decker.

Step 4: A Bit of Wire...

Picture of A Bit of Wire...

Finally we have some 14AWG high flexibility silicone wire from another RC company.

Just had this lying around and I only needed about 3 inches so let's call it free.

I would recommend using good quality wire here. Your battery will only be as good as the weakest link. I prefer not to have any weak links. This will also be a likely spot for a meltdown if your wire is not up to the task.

Step 5: On to the Assembly

Picture of On to the Assembly

I paried the cells and bound them with electrical tape just to make them easier to solder together. These buggers are a little hard to hold on to.

Don't forget to tin both ends of the battery before you try and attach the bars. A drop of flux and a drop of solder, not too much though.

I should mention that you will need a pretty serious soldering iron to get this job done. Don't overheat the battery...kind of a catch 22 here.

Step 6: Now the Tricky Part...

Picture of Now the Tricky Part...

After getting the battery assembled I removed the electical tape. The bars are very rigid and have no problem holding the pack together. Soldering the bars on and getting everything to line up is the hard part. Be patient.

The real tricky part is the cell that sits on top of the pack.(red wire attached) This top-most battery sticks up into the shank of the battery case. The little black plastic bit houses the stock connectors that mate with the actual drill and save that and be careful not to brake it.

The top battery needs to be attached to the battery direcly below it and sit slightly offset. B&D accomplishes this with another plastic part that I tossed. I used one of the stock battery bars that I pulled off the stock battery pack since they were thin and flexible. Both batteries were soldered to the sock bar while they were sitting next to each other. Then, to move the one onto the top, I just folded the battery bar in half...clear as mud...I guess I should have taken a picutre. Finally I wrapped the bottom of the top battery with electrical tape to prevent any shorting.

Step 7: You're Done!

Picture of You're Done!

Well, that's it. Took about two hours from start to finish and it went back into the case quite nicely. The Novak battery bars came with stickers. I love that, so I put a Novak sticker on this one so I would know which pack was my uber pack. Charged it, put it into the drill and it runs like a champ.

You can hear the difference compared to the stock battery. This puppy is just begging for some heavy drilling. Time to pull some screws out of a big crate.


mbone08 (author)2017-06-02

Great idea ! I have a ton of drills that are useless, and I didn't know what to do with them.

Thanks !

Marcel B.

erichtg (author)2016-04-10

Save yourself a serious fire! There is a reason the original batteries were wrapped in paper. Put paper insulation (or some other insulation that won't melt) between neighboring cells. In the case of an over-heated battery the plastic insulation of your batteries will melt, allowing cells to short and catch fire.

fantacmet (author)erichtg2017-02-16

The entire bottom and side of a sub c cell is the negative electrode. There is no fire danger here. Only that nub at the top center is positive. I like the author am an old rc guy. I still do it.

H0s3h34d (author)fantacmet2017-03-30

These batteries are in series. If one case touches another, you have created a short.

ClaybornL (author)erichtg2016-07-30

I'm pretty sure the man is aware of that, as he said he built as he said he built them and his RC racing days but you've got to admit It's gotta have some kickass power just don't overheat it

pwray1 (author)2016-11-15

just to clarify on the size of the battery 18650 which you will find in most laptops , The numbers relate to 18 the diameter of the battery 65 is the length of the battery 65mm and the 0 signifies it circular in shape

stephen.casto.9 (author)2015-02-19

Battery bars are not needed, you can just cut up some tin or copper sheeting. Also, the cardboard tubes were for heat displacement and wear to prevent shorting, so you need to use them.

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.

betterways (author)2013-11-06

This is Good to know stuff. How many other batteries have you taken apart? Are they all made up of common AA, AAA, C, D batteries? I just recently saw a tip that a six volt battery is filled with 30+ AAs. And if a rechargeable one is filled with rechargeable AAs, then you could get a great discount buying them that way.

That video has been round for years, and it's a fake. 6-volt lantern batteries really have just 4 Uber-large F (longer than a D) size cells in them. Pretty much all drill packs use sub-C size cells which means they're the same diameter as a C cell but shorter. Lithium-ion drill packs use 18650-size cylindrical cells that look like giant AAs in terms of proportions but are much fatter and longer. Same size that is used in laptop battery packs.

chrispook (author)2012-09-15

Hi, I've got a cheap 18V battery pack that stopped charging and I'd like to rebuild it according to your instructions. When I opened it up I found a polyfuse in the middle of all the cells labelled JRM A55, which had shorted out. Should I retain this or replace it?
If I uprate the cells will the original charger handle the power or do I need to look at a new charger too?

mickmnr (author)2011-11-03

Hi, I read a fair bit about this topic here as I'm interested in having a pack to run a few cordless tools I have (mainly old drills 12, 14 and 18 V. and a edge trimmer) I also found on the net a site "Rambo Battery" . I seem to understand that it is actually possible to have a "half cordless" tool (that is with a short lead from the pack / porta-pack to the tool, which I think would be fine in most situations). But I don't seem to see any provision for a charger for these contraptions!
I read that the tool does not care where the power comes from and I like the idea of Lithium (rechargeable type) batteries.
Where I live in Sydney Australia they don't seem to have any idea about such alternative ("they" are tools suppliers, Electric retailers, and even battery businesses, such as battery world)
Here in this thread, one get the impression that is rather easy (with some basic idea) to build such apparatus, but it makes me wonder; for instance I have a Black and Decker cordless drill only a few years old but that doesn't seem to have its original battery available anymore and with a battery replacement (mostly out of stock!) and for which there is a very tinny warning: "will not work with original charger"!
My father had an interesting saying "I'm not rich enough to buy cheap things"
I have tried similar "alternatives" with refilling my own printer cartridges, but eventually gave up the idea although it was indeed a cheaper option but at a cost although not monetary. I wonder if contemplating this battery power alternative falls in the same category.
Just the same the idea of a universal pack for cordless tool is indeed very attractive.

CATX20 (author)2010-02-17

Hi, my cordless tool uses 1.2ah sub c cells would this matter if i replace them with 2.0ah sub c cells or would this damage the tool?

mikej_w (author)CATX202011-10-27

A change in Ah - Amp-hour - and will not hurt your tool. If the cells fit, AND are the same chemistry AND are approximately the same voltage, you will be fine.

The biggest danger for the tool is to have too high a voltage, as in heavy use the motor may burn up.

The other problem is with the charger. Your charger is very specific to battery chemistry. Each chemistry has it's own needs. NiCd is the simplest to charge. Hydride batteries are more complicated to charge, and a Nicad charger will charge them but they will have a shorter than desired battery life.
Lithium cells are great, but they need a precision charger. The voltage per cell is much higher, so you could possibly put in fewer of them, with larger Ah to get better battery life per volume.

You could possibly replace the guts of an existing charger with an off the shelf charger from the R/C market to take advantage of these cells.

Oh. The simple answer is just to keep the voltage sane. > Ah won't harm the tool.

Murch77 (author)2011-10-26

I get a kick out of all the RC car products... I thought the exact same thing when I opened up my drill battery!! I have some 3300 Mah NiMH matched cells from an attempt of getting back into racing that are just sitting in storage... They're going to need some attention first, but I might build some "hot rod" batteries!!

arpruss (author)2011-08-21

I wonder if using Wire Glue would work for the tabs? I don't know how well it stands up to the temperatures batteries reach.

motor137 (author)2011-05-27

I have built approximately 6/7 battery packs using the solder method. I typically dope and tin both contacts. I buy about half of my subC cells with the tabs to reducing the amount ofhard soldering.

I have done a fair amount of soldering in my day and have been cautious about overheating the cells, although Ihave messed up few. Never had one explode or anything.

Hears the deal, recently was at Battery Plus and we all know that they pack batteries with a spot welder. I was explaining how and what I was doing and he said he was a fireman and he knew of someone that had a cell explode and burned up his house... He said it was extremely dangerous to do without a spot welder. He would do them for $$$. Now was this a scare tactic or what??? I have a case of SubC cells sitting in the garage wondering?? hmmm comments please. Oh I am using a temperature controlled soldering pen sith a flat screwdriver type end.

archer6817j (author)motor1372011-05-29

That sounds like a scare tactic :) Like I said in another response, RC enthusiasts have been doing this for decades. Just don't overheat the cells :) Any tool, used incorrectly, can lead to injury. Just be smart!

motor137 (author)2011-05-27

ok, been building my packs witha Weller Solder Station, pen. I can adjust the temp and the tip,usually used the screwdriver blade tip. Any idea what temp you think is ideal?

archer6817j (author)motor1372011-05-29

The short answer is that you should use the "right" temperature :) It's best to solder batteries hot and fast. You don't want to apply heat for a long time and "soak" the battery.

tallman2009 (author)2011-05-03

These instructions to rebuild a battery will work, but there are some serious issues with it. Number 1 - you should not solder on the cell terminals. Soldering on cell terminals will ruin the cell and greatly shorten its life. That is why you see spot welds on the original tabs connecting the cells together. You should buy cells with tabs already spot welded on for rebuilding batteries. You also need to be concerned about adding height to the cells with solder etc. so the case will close.
You also need to test the connections as you go so you don't end up with shorted cells or wrong connections. If you want to build a battery superior to the original battery that will run any tool at any voltage, check out the Rambo Battery. The Rambo Battery kit is simple to build and it allows you to run your tools at a few volts over the tool voltage - 14.4 volt tool running at 18 volts for example. You will really enjoy the extra power and speed you get. You can also configure a Rambo Battery using NiMH cells rather than NiCD cells for much more power.

archer6817j (author)tallman20092011-05-29

First, "Number 1 - you should not solder on the cell terminals. Soldering on cell terminals will ruin the cell and greatly shorten its life."

This is absolutely false. If you "overheat" the cells you can damage them, but people have been building high-performance racing batteries for RC for decades by soldering on battery bars.

Second, this sounds like a product advertisement and I'm tempted to flag it as such.

reddnekk (author)2011-02-27

Need some advice. I have every 18v. tool Ryobi ever built--bot first ones in 1993, and they still work fine. But the batteries--have about a 9mo life if used heavily; price has gone from$20 to almost $50 in the past couple of years. So had about 8 bad batteries on hand. Now Harbor Freight 18v. batteriest are dirt cheap--have paid as low as $6. So first took guts out of Ryobi battery, replaced them with guts out of Harbor Freight battery. Finally woke up, and now just take the top stem part off the Ryobi, do the same to the Harbor Freight battery, then connect the wires from the Ryobi to the battery pack in the HF, and glue (and tape) the Ryobi top to the HF bottom. Am using the Ryobi chargers (have six) which have a trickle charge and a fuse inside, and so far everything seems to work OK. Now, am I doing something I shouldn't? Am I risking fire or tool damage? Need to know, because am now working on plugin adapter for these tools so can run them on house current.


chenxinghao (author)2009-06-12

What type of screw drivers did you use to losen the screws and open the case? My Craftsman 19.2 volt battery seems to require a special tool similar to torax but there is a little dot in the middle that is preventing any tool to get in to the spot.

allen (author)chenxinghao2009-07-04

You need "security" fastener bits. Harbor Freight has them for pretty cheap - or

Unfortunately there are quite a few slightly different bits and if you don't have the right bit you quite often can't get the fastener out.

Deguacas (author)allen2011-01-17

When all else fails, use a dremel with a small cutting blade (carefully!) to cut a slot on the head of the screws, then use a reglur flat blade screwdriver

sojakai (author)chenxinghao2010-02-22

A trick I learned from a buddy who works on arcade machines told me to take a screwdriver, put it against that little post and wack the end with a small mallet/hammer. It breaks the pin out and allows you to use a standard bit for removal. Apparently, he does this so often that he carries a mallet around.

Gotta love those "Fine Adjustment" tools.

putnamcs (author)2010-06-11

Great Instructable. I too was frustrated with the cost of replacement batteries (for me it was my Craftsman drill). I didn't go all the way to 'hot rod' my battery pack, but your Instructable gave me the confidence to tear into it, find the dead cell, replace it and get my drill back from the dead. My battery cost $4.58, locally, at a store called Batteries+. That was the entire cost of the repair. One cell and solder I had on hand. Bravo. Thanks for taking the time to document this Instructable.

pastorm2 (author)putnamcs2010-10-14

Can you please tell me how to identify the dead cell ?
Thanks !

matroska (author)2010-08-26

Protip: Did you know you could do the same thing with laptop batteries? Ha! Except, in laptop batteries it's a less common battery type, normaly the 18650. If you have some dead laptop batteries, try and open them. You will notice batteries that will look like AAs but that are longer. Once you identified the battery type (again, usually 18650) you can find a place to order new ones online and replace the old cells.

wrksnfx (author)2010-07-17

If your skills at soldering has you trembling there are places like that if you take in your dead pack they will take it apart and see how it's put together and build you a new battery bundle my brother did this with his Vietnam issued metal detector.

sharlston (author)2009-11-01

you will not be able to get shocked by a drill battery

Russell Nash (author)2009-10-03

This is the place where you're most likely to screw it up. I avoided the problem by buying the batteries with solder tabs already attached.

Poppy#1 (author)2008-12-05

Can I use Nimh batteries instead of Nicd? I am trying this with a Dewalt 18v battery pack.

syruss (author)Poppy#12009-09-29

make sure ur charger will charge both Nimh and Nicd batteries

Poppy#1 (author)syruss2009-09-30

Thanks, I have pretty much given up on this. It can be done easily enough though and by the time I add the cost of batteries, I have found that I can buy replacement refurbed powertool batteries for about the same. It was fun to do though and easy. Thanks for the help.

irishjim68 (author)2009-08-25

You could always VERY CAREFULLY drill out the post in the middle of the fastener, then use an "Easy Out" to get it out of the hole and replace it with a phillips screw of the same size.

eight (author)2007-05-12

Hey archer6817j,

Now this is a real instructable.

1. It is a genuine project
2. It justifies the time it takes
3. It saves money and the planet.
4. It is well documented.
5. You have included relevant links.
6. It gets eight's approval. (The sticker is in the mail, mate !)

Here are a few thoughts n the project and various comments/questions...

I use RUSTEX (35% phosphoric acid) for tinning wires and metal tabs when soldering. It is cheap and can be used for pacifying rust on cars and steel.

You can buy very wide heat shrink tubing to hold packs together.

NiCd cells can dump much more current in a split second than NiMh.

NiMh needs a special charger.
If you use a NiCd charger it will work to a point... but you wont get the depth of charge and neither Charge or Batteries will last long.

The biggest "D size" cells I can find locally have 9Ah capacity. (9000 mAh)
These wont fit in this project, but man -o- man what a charge life :)

Many older laptops used a "A" cell ( 2.0 Ah or 2.2 Ah ).
"A" cells are same length but bigger Diameter than "AA" cells.
Since "AA" cells now have 2.6Ah capacity, you can make lighter packs when rebuilding.

FYI, Duracell make 1.0Ah "AAA" NiMh.
I have been quite busy modding various torches and other items with these smaller cells.

Sorry for a long post... Lots to say : )

Ian01 (author)eight2007-07-28

This is an A cell, big and rectangular

eight (author)Ian012007-07-29

No mate. An "A" cell is like an "AA" cell but slightly larger diameter. I got mine from an early (Pentium 3) laptop power pack.

lilpepsikraker (author)eight2009-08-08

For anyone still reading, that is NOT. an A cell. It is an 18650 cell. Look it up.

eight (author)lilpepsikraker2009-08-09

Wow... I said that 2 years ago.

Mud Stuffin (author)2009-08-04

Exactly the same kind of drill that just died on me. Thanks for the info!

dlfynrdr (author)2008-04-24

If you mess up and overheat the batteries while soldering them together, how obvious is the results? Does the thing blow up in your hands, or do you just find out you can't charge the sucker? Or is there a quick way to tell with a multi-meter?

archer6817j (author)dlfynrdr2008-04-25

Excelent question and I have no idea. I would imagine a minor overheat would harm the battery internally and if you had a major overheat it might rupture. You should try to get the joint soldered in the first go. If you mess up and have to try again it's best to let the battery cool off a bit. My rule is if it's too hot to touch then it's too hot.

Poppy#1 (author)archer6817j2009-02-10

archer, how easy is it to get the top battery out of the casing without breaking it. I am trying to re-do a DeWalt 18v drill/powertool battery and would appreciate any info that will keep a klutz (me) from busting everything.

archer6817j (author)Poppy#12009-02-10

I think my battery was just held together by three screws. There might be some glue involved. Caution is advised since the plastic the battery case is made of is probably brittle and will crack/break if you do too much prying.

Poppy#1 (author)archer6817j2009-02-10

I think I will be able to unsolder the gizmo from the batteries. The tabs they have on them are pretty long and I can pull the battery part way out of the fitting charging thing, but I am guessing that I will be able to unsolder it and remove the 1 battery and replace it that way and then solder the tabs to the pack of batteries after that. Will let you know. Thanks for the answer so quickly.

Astinsan (author)Poppy#12009-06-09

The batteries are welded to those tabs. It is a special two prong spot welder. The prongs look like two black pencils with wires going to a transformer. You can however use batteries with the tabs already attached. This makes the connection easy to soldier

Poppy#1 (author)Astinsan2009-06-09

Thanks for the input. My problem seems that I cannot get the soldering gun hot enough. I kind of gave up on it and gave it to my son (the Mechanic, Computer guy in the family) to see if he can make it work for me.

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