Introduction: Don't Throw It in the Landfill: "How to Repair a Cordless Drill With Broken or Missing Battery for About $3 (or Less)"

Picture of Don't Throw It in the Landfill: "How to Repair a Cordless Drill With Broken or Missing Battery for About $3 (or Less)"

Many people have the battery in their cordless drill go out, and simply throw it away. In fact I obtained 2 cordless drills with missing batteries at a yard sale in a free box, as you guessed for free. This instructable shows you how to turn a cordless drill with a missing or broken battery back into a working drill again.

The materials you will need for this are: (see above picture for images)

   • An AC 120 volt to DC 12 volt transformer or AC 120 to DC 18 volt transformer, these are the two main power supplies for cordless drills, however if your drill says another voltage then get the appropriate transformer for that drill. Basically you need a power supply that changes 120 volts AC into your drills voltage DC. ( This is about the only thing that will cost you money assuming you already had the drill or got it for  free)

   •  Screwdriver to disassemble the drill

   • Cordless Drill (obviously)
  • Electrical tape

Step 1: Take Apart Your Drill

Picture of Take Apart Your Drill

This part is simple just remove the screws (save them!) and separate the two pieces of your drill carefully. You want to separate the pieces carefully, so you don't drop any mechanical pieces out of the drill. This will be probably different for your drill than mine.

Step 2: Cut the Wire Between the Trigger and the Battery Terminal

Picture of Cut the Wire Between the Trigger and the Battery Terminal

Between the battery terminals and the speed trigger there should be a wire, cut this wire close to the battery terminals and use wire strippers to strip about an inch off of it. See picture for further illustration on this.

Step 3: Cut the Plug Off of Your Transformer and Strip Wires

Picture of Cut the Plug Off of Your Transformer and Strip Wires

On your transformer if there is a circular plug (called a barrel jack), cut the 2 wires leading to it. Next strip about an inch off of the end of the wires leading to your transformer. Then twist the wire strands together. See the photos for a step by step illustration.

Step 4: Splice the Wires

Picture of Splice the Wires

Image 1:

Now that your wires are stripped to around the same length, cross them in an X form, where the center of the x is about midpoint of the 2 stripped sections of wire

Image 2: 

Whichever wire is on top (closest to you) bend away (or back) and then down, the wire will make a upside down L shape around the back wire.

Images 3 and 4: 

Now take the other wire, bend it towards you (or forward) and then down, twisting it around the first wire, making a M shape

Image 5:

There are two directions to twist, you do not want to twist the entire wire, just the splice. I recommend using your thumb and forefinger of each hand to twist the wire. One wire will go clockwise (or towards you) the other wire will go counter clockwise (or away from you), pinching hard, twist only the spliced section, slowly moving towards the insulation with both hands if you are using solid core wire, or thick gage wire once you get near the ends, I strongly recommend you wear gloves or use needle nose pliers to finish up the twist if you got close enough to the same length of stripped wire, and made your X close enough to the center of the two wires you should end up with both ends of the wire running out just at, or before the start of the insulation and a super strong splice.

Image 6: 

Wrap electrical tape around each set of wires individually being sure to cover any exposed metal so that it will not touch the metal from the other wire and then tape the two bundles together to make a clean, finished, and insulated job that will not short out.

Step 5: Reassemble Drill

Picture of Reassemble Drill

This step is pretty self-explanatory, put the screws back in to where they belong and tighten them. This will be probably different for your drill than mine.

Step 6: Test

Picture of Test

Another easy step, test the drill by plugging it in, pushing the trigger, and possibly drilling something. The picture is a file photo not my drill lol.


ChelseaTE (author)2017-03-04

I made it! Used the original battery charger - 18 V for an 18V battery - but I'm not sure it runs any faster than it did the old battery. Which is to say slowly. What am I missing?

mykiscool (author)ChelseaTE2017-03-04

Hello Chelsea, I am sorry to hear that this isn't running well for you. What is the amperage on your charger? Could you supply a bit more information about your drill type and charger. In the case of this project, the most important value when selecting a power supply is voltage. Current does come into play however, and while it will still work, until the motor reaches maximum power draw, increasing the current increases the speed. Some power supplies however, have very little current and are designed to trickle charge batteries.

Additional information in regards to batteries/charging: Different battery types have different max ratings called C ratings. The C rating specifies the charge and discharge rate of batteries.

sxcay made it! (author)2016-10-13

Problems with the power, but it does work. I will have to use a more powerful transformer.

mykiscool (author)2016-05-06

It's possible, but there are a few things to think about. In an electrical circuit you have voltage and current. Current is the part that generates heat in a circuit. Voltage and current are proportional. So, if the motor is designed to work at 12v and you run it at 19v, it will go faster and have more torque, but it could overheat. You could solve this by using a voltage divider or regulator to lower the voltage, or you could use a resistor to limit the amount of current that the motor can draw. If you know the current that the motor is designed to operate on, you could then use ohms law to figure it out. (VCR) voltage = current x resistance. Depending on the motor, it may be able to withstand 19v. I would recommend monitoring the temperature though.

OhL1 (author)2016-05-05

can i use a 19v adaptor to power 12v drill?

JacobK16 (author)2015-08-01

I have a Black&Decker CD1800S 18 volt drill. I bought this adapter to convert it to corded: I connected everything and the drill ran, but it was very slow and weak. I'm not sure how to make it work well.

IhsenS (author)JacobK162015-08-20


I Convert a battery of Cordless drill to ATX power supply

mykiscool (author)IhsenS2015-08-20

I love atx power supplies. They have good output, steady voltage and a variety of common voltages. Highly recommended for most projects.

mykiscool (author)JacobK162015-08-09

It is slow because the power supply is very small. That power supply has less current than a USB port. The amps aren't critical, but it's better to have high amperage because if you have the right voltage it won't draw too much power anyways. If you get something in the 3-5 amp range it should have a lot of power.

JacobK16 (author)mykiscool2015-08-10

So, you recommend an 18 volt adapter with more amps?

Cmb173 (author)2014-12-30

This is my first time doing anything like this, so forgive me if I sound like an idiot. In step 4, the first 2 pictures look like you are connecting the transformer to the wire on the drill, but the next 3 images look like you are connecting the 2 wires of the transformer to themselves. Can you please explain? Thank you

mykiscool (author)Cmb1732014-12-30

It's better for you to ask first. I'm happy to help you out with any questions.

Connect the drill battery connections to the appropriate transformer connections. The transformer connections do not go to each other as this would short and could possibly kick your breaker (not a big deal just reset from the electric box outside your home or better yet plug projects into resetable power strips.)

RichardLapare11 (author)2014-10-18

It works, but no power !!!

What size transformer are you using? It may require a bit more current than the transformer is willing to supply. You may notice the motor starts out slow and slowly accelerates. This would be because the motor draws more current on startup then when running. If it's a 12v drill you may try testing with your car battery and see if the power is better.

kretzlord (author)2013-08-18

does the limited amp rating on the dc adapter limit the power you get with the drill?

eszy (author)2013-05-13

Lmao. I. Love. It. I. Made all my old drills. Works like. Like. Hummm. Pulling a wagon with a hamster. He he he

ninjatails (author)2013-04-24

If you have a soldering iron, I'd recommend soldering the splices--otherwise they can heat up and cause problems.

weezulman (author)2013-04-08

You might want to add that the wrapped wires need to be wrapped with tape separately and than together. Some people don't grok short circuit.

mykiscool (author)weezulman2013-04-09

Ok, thanks for the feedback. I've added it. I always appreciate constructive criticism that will help me become a better instructor.

heathbar64 (author)2012-07-19

I have a few old defunct battery drills around. I was thinking of using the battery chargers that came with them and a jumper wire directly to the drill. I know charging voltage is a bit higher that battery output, but hey! more power.

Ian01 (author)heathbar642013-01-13

I foresee two potential problems: first the battery charger might not supply enough current (especially if it takes longer to charge the battery than to discharge it), and the battery charger might be designed to monitor the battery and charge it in an optimal way (probably not for NiCd, probably for NiMH, definitely for Li-ion). You might be able to separate the power supply and charge controller parts of the charger and use just the power supply.

lemonie (author)2012-07-21

The picture is a file photo not my drill lol.

-Does your drill actually work, or is it difficult to photograph while you're using it?


mykiscool (author)lemonie2012-07-21

It is difficult to photograph while I'm using it, because I don't have anyone to help me. The drill works very well.

macrumpton (author)2012-07-21

It would be a good idea to monitor how hot the charger is getting if you are doing a lot of drilling. Battery chargers are made for supplying a relatively low current, and running a drill off of one may overload it and make it melt or catch on fire.

scraptopower (author)2012-07-19

This is good. I'd suggest one of those springy coiled wires to connect it up for conveneience. Also worth noting some wall adapters put out AC not DC.

mykiscool (author)scraptopower2012-07-19

Oh yeah thanks for adding that, sorry it's my first Instructable I tried to be thorough, but missed that detail.

achilles (author)2012-07-19

I really like the idea, but finding an appropriate AC/DC transformer could be difficult.

1. MATCH YOUR VOLTAGE - if the voltage of the \transformer isn't correct for the drill it may not work, or you know... explode

2. Having enough amps - A lot of drills are listed as 1.2-2.4amps, but peak can be significantly higher, so you may experience loss of power under strain.

3. I would look into (and have been thinking about) using a universal laptop charger which can be found for around 15$. They have adjustable voltage and often higher amperage (around 5amp).

*** Do NOT take this as definite advice, I'm a biologist not an electrician

mykiscool (author)achilles2012-07-19

I completely agree with you, that is why I have specified that the transformer must be 12 or 18 volts depending on your drill, and showed an image of the transformer I used. I appreciate your comment, thank you for taking time to notice that.

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