Mod a Cordless Power Tool Battery to Run With Wall Current




About: My goal in life is to be a chemistry professor, because a) I've had lots of awesome influential teachers b)Bill Nye kicks ass c)I like things that burn, pop, explode, fizzle, and bubble.

NOTE: I wrote this 'ible before I had a comprehensive understanding of electronics. This is a rather bad idea and will most likely wreck your battery. It seemed intelligent at the time. Oh well, live and learn.

Adding a jack to the battery of a cordless tool so you can run it off of wall current and keep it close to full power all the time. This might not be the brightest idea to do with NiCd batteries, but if you have a skunked battery you can't lose much.

I decided to do this project with the Black & Decker Firestorm 18V system, but you could do it with nearly any cordless tool set.

Things you'll need:
-Cordless battery and charging unit
-Soldering iron and solder
-Wire strippers
-Electrical Tape
-Something to dismantle your battery (In this case Hex wrenches and Torx bits)
-Two wire quick-disconnects (they usually come in male-female pairs)
-Power drill and bit
-Knife or x-acto

You may also want:
-Hot glue gun or epoxy

Step 1: Dismantle Your Battery

-This will void every sort of warranty you could hope to have. Proceed at your own risk
-Discharge your battery before working on it. This should be a no-brainer

Each battery is made differently, so I can't give specific instructions on how to take it apart. Mine involved really annoying hex screws that refused to budge. Then I realized they were Torx - hey this is a learning experience. So I got a Torx10 bit and took it apart.

You should be left with two halves of a case, the cells, and possibly some springy do dads.

Step 2: Find Your Anode and Cathode (+ and -) and Wire the Quick Disconnect to It

Locate your anode - this is going to be usually white or red. If you've forgotten your cell setups, this is the positive terminal. In my battery there was a white wire for the anode and a common cathode (a plate that just connects all of the cells' cathodes).

Drill a hole in the side of the battery casing so that it's convenient to run a cord out of.

Run the wires of the quick disconnect trough the hole. It doesn't matter which one you use, as long as you use the opposite one for the wall unit end. For my example, I used the female, so the wall unit will be male, so on and so forth.

Wire positive (red or white) to positive and negative (black) to negative). Solder the wires, being careful not to damage the cell.

Step 3: Reassemble Your Battery

Put the battery back together. You will probably have to force it a bit in order to get the wires to fit in the casing. Also, make sure to put back any springs or things that lock the battery to the tool. I used QuikGrips to hold it together while putting the screws back in.

Step 4: Modify the Wall Adapter

Now to modify the power cube to attach to the battery. Since you're going to be drawing a bit more current, you will might have to replace the original cable. Mine was mysteriously cut a while back, so I used the opportunity to upgrade to an extension cable.

Cut the power cube from the part that clips to the battery. If you're going to replace the cord, leave about 1.5" on the power cube end. Otherwise, cut it 1.5" from the battery clip and skip to soldering the quick disconnects.

If you decide to replace the cable, cut it to the length of cord you want. About six feet is good for most uses. On each end, make a cut about 3" from the end so you can open the outside case like a pea pod. Pull the wires out, and cut out the ground if there is one. Cut 1.5" off of the black and white wires and strip the last half inch. You should be left with two 1.5" wires with the last third stripped.

Strip a half inch of the wires from the power cube, and solder those to the ones coming out of the cable. Do the same for the quick disconnect (male) at the other end of the cable. Wrap each of the interior wires with tape, tuck them inside the cable, and tape all around that.

If you still have the battery clip, you can solder on a (female) quick disconnect so that you can still use the charger as is by plugging the clip into the modified wall unit.

Since quick disconnects usually come in pairs, you might have a leftover male adapter. You can use this as an auxiliary charger, say if you wanted to charge from a lead acid battery, or zap it with an arc welder to reset the cells.

Step 5: Finished! - Using the Power Tool

The battery and charger should be all set now. NiCd batteries are a pain in the ass sometimes because of dendrites and charge memory and stupid stuff like that, so I think the best way to use this system is charge the battery full, then use it with the cord most of the time. The wall unit as is doesn't have the capacity to run a power tool by itself, but the fully charged battery gives it the extra oomph. In between usage, the battery recharges, effectively allowing you to use the tool at full power all the time. Of course, if you have it running nonstop for long periods of time, it's gonna run down; furthermore this is a bad idea because you might overheat some of the components.

I've found that with moderate usage my tools have, if anything, more power than they did before. I haven't put them through serious testing yet, but when I do I'll post an update.

Pretty much the main reason I used the original batteries is they keep the electrodes in place. Given more time and money, I would have gotten some 18V capacitors and replaced the cells with those.

This is my first instructable so let me know what you think!



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    25 Discussions


    7 years ago on Step 5

    Just wanna know the rating of the cube power supply, i.e. volts, amps and how much wattage it can handle.


    11 years ago on Step 4

    I have a 100W ( H4 bulb ) portable Flash Lights that has a 12V Lead Battery and it takes ages to charge ( 20+ hours ) and i would like to find a power drill battery that has a big capacity and takes quicker to recharge and mod it to fit in the butt of the flash light where the old battery is now. Most power drill batteries that i seen have 3 or 4 connectors, how do i know what one to use ? I do not want to damage the battery. Also ... can I step up to a 18v / 24v / 36v battery or can that burn the bulb ?

    2 replies

    Reply 11 years ago on Step 4

    You'll need a voltmeter to figure out what each of the different leads are. I wouldn't use a larger voltage battery, you might get away with 18V without burning it out instantly, but you'll definitely shorten the life. Have you thought about re-celling the lead acid battery? You could hollow out the battery case (wear gloves! the acid isn't too bad but the lead will get right into your system) and put in NiCd rechargables.


    Reply 7 years ago on Step 4

    great article. i'm curious about the "wall outlet doesn't have enough power." Can you say more about that? i have a computer that uses 90 watts and runs off a wall outlet (dell latitude). it seems we should be able to get around that limitation. thanks, nice article.


    8 years ago on Step 4

    How many m/a transformer do you need for 14 V or 18 V ?

    How do you caculate this ?


    9 years ago on Introduction

    The adapter will spend most of its time charging the batteries, there isn't much useful power from the adapter to run the drill. But you can do it the right way. I've run power drills at maximum speed on just about an Amp of power alone successfully. No batteries, no pollution. 

    3 replies

    Reply 9 years ago on Introduction

    You can use solar panels, windmills, or other renewable energy producers to power your drill directly. If we want it, power plants can be made into non polluting ones.


    Reply 9 years ago on Introduction

    Totally - I'm all for that :p

    But that's not the dirty facts on the ground. >75% of power produced in the US is fossil fuel driven :/


    12 years ago on Introduction

    It's also important that you select a wall adapter that meets your amperage requirements. You want to have at least what your drill will pull.

    5 replies

    This is very true. If you are going to be drilling into hard wood or concrete, you will be putting a large load on the drill. If you are using the drill in hammer mode, it will be even higher. A silly 1 amp wall wart from wal-mart won't cut it, you will need maybe 3 or 4 amps... At this point, i recommend buying a corded drill.

    I have drilled into concrete, thick steel and everything with just an Amp of supply. Make us wonder why we need polluting batteries.

    if you left the battery intact, it will pull the power from the battery, along with the wall-wart, but for that, you'll need a diode


    10 years ago on Introduction

    Same problem here, I wanted to use my battery power drill, mostly for driving screws in wood. Dead battery after some 2 years, drill still OK, has real low gear and lots of torque. Because the large current none of my smaller electronic power supplies would work, till I remembered a few older, standard PC supplies still lying around, that typically have 12 volt at 10 or more amps. I gutted a battery pack, connected a 12 ft. cord of about 14 gauge strength and in my workshop I can do all the screwing I want. Even so sometimes when the drill stalls, the power supply turns off, but will reset after switch off and on again. Some PC supplies need a little load at the 5 volt, to surely start up, I connected a small bulb of 6 v 1 amp to the 5 volt. This works best with the older XT or AT power supply, the newer ones, ATX, need a signal from the mainboard, which also can be arranged of course... One time I had some heavy work outside, miles from any outlet, to assemble a wooden swing-gate, there I used a few croc-clamps and my car battery, worked fine! tokkoh


    11 years ago on Introduction

    That is a great bran-new idea.This is andy from China, we are a replacement cordless power tool batteries manufacturer. Wish can communicate with you all about cordless tool batteries. Thanks and nice day!Guys.