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!

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Step 1: 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

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

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...

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

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...

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!

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.

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    95 Discussions


    2 years ago

    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

    1 reply

    Reply 1 year ago

    DO NOT USE 18650 batteries for this; they are lithium cells, are rated at 3.6 - 4.2 volts instead of 1.2 and need a different kind of charger


    2 years ago

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

    Thanks !

    Marcel B.


    3 years ago

    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.

    3 replies

    Reply 2 years ago

    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 fantacmet

    Reply 2 years ago

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


    Reply 3 years ago

    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

    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.


    5 years ago on Introduction

    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.

    1 reply

    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.


    7 years ago on Step 7

    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?


    7 years ago on Introduction

    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.


    9 years ago on Step 7

    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?

    1 reply

    Reply 7 years ago on Introduction

    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.


    7 years ago on Step 4

    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!!


    8 years ago on Step 5

    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.


    8 years ago on Introduction

    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.

    1 reply

    Reply 8 years ago on Introduction

    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!


    8 years ago on Step 5

    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?