Cordless Tool "Repair" / Renewal




This simple tutorial will help you reclaim your once battery-powered harbor freight tools by adding a DC power supply. The tutorial should apply to just about any cordless tool, just make note of the battery voltage / amperage on your tool. The main advantages to this method (as opposed to others on the site) are style/clean fitting, and parts availability.

While this tutorial isn't groundbreaking, it may give you the motivation you need to get your broken cordless tools back up and running.

Harbor Freight and I have a Loove hate relationship. Half of the stuff they sell is inexpensive and worthwhile, the other half is inexpensive and junky. If you shop there, you know what I'm talking about.

Some of the junkiest items they sell are the cordless power tools. 9 times out of 10, the batteries die quickly or were never good to begin with. Sometimes its the fault of the charger or AC adapter, sometimes it's the "rechargeable" batteries. In any case, they aren't worth picking up unless you're in the mood to gamble.

If you have by chance made the mistake of buying one (like i did) and can no longer use the battery for whatever reason- read Step one.

Step 1:

Get Yr supplies together.

You'll Need:


-Cordless 18-24v Power tool (I used a circular saw)
-2 short strands of wire (I forget what gauge I used but most should be fine)
-1/4th inch male and female audio jacks
-18-24v 2A Power Supply (I used a salvaged epson printer power supply rated 24v, 2A)


-drill / bits
-hot glue
-screwdrivers (one philips, one flathead)
-solder / soldering iron

Step 2:

Now, take the battery apart, it should be held in with 4 screws on the top.

Pry it open GENTLY with a flathead screwdriver. Take the batteries and contacts out (they will be attatched)

now bend or cut the leads off the top batteries, but leave some metal to the battery contacts, you need enough to solder wire onto them.

remove the regargeable cells. (then recycle them if you have the means)

Now, Hot glue the contacts into place so they'll stay put. Be sure not to get much hot glue on the bottom parts of them, you need to solder wire there.

Step 3:

Now, solder 2 wires to both contacts. Be sure the wires are long enough to reach the bottom part of the battery where you will solder them to the 1/4th inch female jack.

Drill a hole in the bottom of the battery to fit the 1/4th inch jack.

Insert the 1/4th inch jack then solder the two wires to each lead. Make note of the polarity (+ / - ).

I used hot glue to fasten it in.

Put the contacts back into the tip of the battery and re-assemble your battery.

Step 4:

Strip the wires of your power supply and then solder them to the leads of your 1/4th inch MALE jack.

Be sure to make sure the polarity is correct, just put + to + and - to -

If you get it wrong, it should be ok, the tool will probably just spin backwards.

(Just swap the wires on this tip so you dont have to open your battery again.)

I used a male jack with a screw on plastic shield and held it in place with some hot glue.

(there's a different picture in the intro)

Step 5:

Now, plug everything up and use your tool again without worrying about a cheap-ass battery that might die after 15mins.

Note- it may take (literally) a second or two for things to start spinning because the AC adapter needs to charge up. no biggie 4 me.



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17 Discussions


1 year ago

I would suggest changing the male/female sides of the power supply. The female should be the hot side and the male mounted on the tool for safety!


1 year ago

Great job! Thank you for the post. If anyone need awesome brandnew replacement battery for your cordless tools. Go and shop on loopower.


Very nice. I had a printer power supply that wasnt steady. It sent power at about one second intervals. I like the connector. Super convenient to not always be tangling up wires. If you were using that circular saw powered by a battery and it lasted 15 minutes that is amazing. My dad has a set of porter cable power tools-drills, sawzaw, circular saw. The drill and the sawzaw you can use for a long time off battery. the circular saw is basically unusable.Not even juice. I dont know if it's even meant for wood. It might be for intended to use for scrapbooking or something.


I think this is a great and simple solution to a common problem. For some reason though, i am always afraid of using audio connectors for power-related projects, mainly for the reason that someone might use it for audio and end up frying their equipment. My fear is completely unfounded but for some reason its still there. Aside from that, do you find that the 1/4" jack stays put?

4 replies

I'd be reluctant to use a TS (tip-sleeve) connector for another reason: one contact slides past the other when it's connected or disconnected, possibly resulting in sparks or a short circuit.

I have one of those jacks in use as a lamp swivel power jack(12V, 1/3A led homebrew light bulb).
holds just fine. "minimal specs" for commercial version of the jack is 1lbs. of extraction force. can be as high as 7lbs.

just fyi, specced at .05 ohm resistance after weathering and ambient humidity.

here's the important part.
Contact rating is 1 A, 25 V DC

So, "the salvaged epson printer power supply rated 24v, 2A" is 100% OVER spec. now, if that was a 12 Volt 1A power supply/drill you'd be "safe".

Staying below that spec should also allow relatively safe "mistakes" since the audio equipment should be either fused, or just plain designed to handle that current without risk of frying you.


8 years ago on Introduction

I like the plug idea, it makes for a clean disconnect. I was considering something like this before I figured out how to repair my battery charger (in my case, the batteries weren't the problem).

My main concern with the direct connection was the balance - have you considered filling the empty battery case with inert weight to make the tool still feel balanced?


8 years ago on Introduction

I would like to try this but I'm curious. 18V at 2 amps seems like it would be underpowered; don't ~5" circular saws usually draw 6-7 amps on 120V ac?


so does the Epson printer cable output DC power? My 16V-32V (three hole) cable is not either cutting off (at 16v) or pulsing/ticking when I turn on my Powermate saw. Not sure what I missed. So essentially, you just connected negative to - and positive to +, no ac to dc converter right?

1 reply

You should probably use another AC to DC adapter. 32 volts is too much for the saw.
Not all Epson power supplies are the same. 

Find an adapter with just ONE voltage listed on the bottom sticker (18v or 19v or 20v or 21v or 22v or 23v or 24v and at least 2A) 

post a pic if you get one and you're unsure


9 years ago on Step 1

it will not fry iether saw or power supply if im running the saw for 15minutes? i want to try dis but i'm worried running 24v dc to 18v motor of my saw  will be damage.

1 reply

9 years ago on Step 5

if doing this mod to a drill, i would recommend mounting the plug in the side of the former battery.


9 years ago on Introduction

If the audio jack is much of a problem, keep it away from small kids and be sure to mention that it's a power jack before you lend it out. Basic precautions ;) I just happened to have one around and i think it looks quite nice compared to other connectors.