Semi-Cordless Drill.

About: Retired Tool Maker ( 1980 ) Retired Mechanical Engineer ( 2009 ) Full time Tinkerer

Hi Gang!

So if you have a battery powered drill, one day you will find the battery pack dead and unable to charge again. I wasn't willing to pay the price for a replacement battery, but just couldn't trash the drill. Once I bought some new cells, but found them the wrong size to fit in the case. I did have a battery from an alarm system that had plenty of power, but it was just too large. So I decided to add a short cord from the cordless drill to the alarm battery, making it a semi-cordless drill. Here is how I did it.

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Step 1: Break Open the Case.

So open the battery case, keep all the parts and screws. Notice where the cells are connected. Make a note of it, or take pictures. Then trash the old cells ( recycle properly please ).

Step 2: What If You Forgot?

So you didn't make notes or take a picture of the connections? Use some test wires on the drills terminals to find what works. Now make some notes!

Step 3: Add Wires to the Old Battery Pack.

Using your notes connect a two conductor wire where the cells were connected. Then drill a hole in the battery case for the new cord and pull the cord through.

Step 4: Cord Relief.

To protect the connections put a wire tie around the cord so it can't pull out of the case. Make it tight and trim off the excess. If it looks OK screw the case back together.

Step 5: New Battery Connection.

I like to use spade connections to the battery. It makes it easier to move to a new battery. Alligator clips could be used for more versatility. If your drill runs backwards, just reverse the clips.


Step 6: Ready to Drill Again!

So there you go. You have a new short cord on your old drill and can now use just about any battery to keep working.

Please work safely and have fun.


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6 Discussions


1 year ago

I've got a couple of cheap old Black & Decker cordless drills, one 12V and one 18V, and both sets of batteries gave up the ghost at the same time (conveniently this allowed me to upgrade to a Makita 18V drill).

As @charles543 suggested, I'm probably going to end up removing most of the drill casing so that I can permanently mount both drills. One in a mini drill press, and the other for drilling horizontally for dowel pin holes.

Ricardo Furioso

1 year ago

Brilliant recycling of old tool. Great Instructable. Thank you for sharing.


1 year ago

Why not run the cord directly into the drill, and eliminate the battery case?

1 reply

Reply 1 year ago

Hello Charles:

By wiring the battery case I can still use the standard batteries if they have a charge.



1 year ago

This is a really good idea -- so good that I actually did this a few weeks back to a cordless screwdriver AND a reciprocating saw. I was in the same position, 12v NiCad pack (screwdriver) and 18v NiCad (saw). Both perfectly good tools and accessories, but unusable due to dead batteries.

Those 17Ah batteries are a beast to lug about, especially up a ladder. I used the smaller 7-9Ah 12v for the cordless screwdriver (way bigger than the 1Ah original), and a set of 3x6v 3Ah batteries in series for the 18v pack.

In each case, the battery/battery pack fits inside a little padded carry-bag to protect them, and make it easier to lug around.

Make the cord long enough that you can put the battery down when using the tool! Otherwise it's really awkward.

Step 3: In my case, when the cells were removed, so was all the support the contact tabs. In one case I had to superglue the contact tabs into place (to hold them), and in both cases I turned the packs upside down, and back-filled the area below the contacts with PVA glue/sawdust and left it to set up. This locked everything in place.

Step 4: Strain relief ... or tie a knot in the cable

Step 5: Watch out for this bare metal connectors flapping about, that's a short circuit waiting to happen :)