Convert Old Cordless Tools to Lithium Power




Introduction: Convert Old Cordless Tools to Lithium Power

About: I'm a former bicycle industry designer turned professional jeweler. I like working with my hands and am happiest when I'm in the shop building my creations. If you need help with your project just let me know!

I have several old cordless power tools and they're all in good working condition. The trouble is the batteries all need to be replaced and the batteries are obscenely expensive. I have a really hard time paying for batteries that cost almost as much as the tool and I didn't want to discard perfectly good tools.

One other issue I had with my old batteries as that every time I went to use them the batteries were dead as the NiMH batteries would self discharge rather quickly, especially in cold weather.

Most modern cordless tools use Lithium batteries and I happen to use LiPo battery packs all the time for other projects so I figured I'd convert my old cordless tools to Lithium power using inexpensive LiPo battery packs.

This is a really simple conversion and the cost is a fraction of what power tool manufacturer replacement batteries cost.

Be sure to check out the FAQ section at the end as Lithium batteries do have to be treated in a particular manner!

Step 1: Tools and Materials

There are only a few tools needed:

Wire stripping tool- I really like this inexpensive wire stripper

Wire cutters

Soldering iron- You could use pretty much any inexpensive soldering iron as this is a very easy job. Mine is an analog Pace ST30 which I purchased used for $100 (I had to look for a long time- new is about $260) The digital version is the ST50 model.

Dremel tool with cutoff wheel (a narrow bladed saw will also work and cuts cleaner)

Battery charger- I really like the Hitec X1 Multi-Charger as it's a smart charger can handle most any battery chemistry but any charger capable of charging multi cell Lithium batteries will do

For materials you'll need the following:

Heat shrink tubing

Wire (14ga is best)

XT60 connectors (these come with heatshrink)

Battery monitor- I really like the inexpensive Hobby King low voltage battery alarm

3s (11.1V) or 4s (14.8V) LiPo R/C battery pack- Hobby King sells lots of different LiPo packs so pick the one that best matches your tool's voltage and available battery space

Step 2: Open the Battery Case

Cut apart the old battery case.

A few cordless tools have battery packs that are bolted together but no such luck with my Makita tools- the battery packs are seam welded shut so they had to be cut open.

To cut open the battery pack I carefully cut around the top edge of the casing with a Dremel tool cut off wheel. Once you get the top of the casing off remove the battery cells (properly recycle them) and keep the empty battery casing.

Measure the inside of the casing to determine how large a LiPo battery pack you can fit inside that closely matches the power tool voltage rating. For my Makita 14.4V drill I used a Turnigy 1300mAh 4S (14.8V) LiPo pack that measures 74mmx 34mm x 33mm and it fit the empty battery casing perfectly. You don't want the battery to use all of the available space as you'll need a bit of room for the wiring and low voltage alarm,

Step 3: Solder the Battery Connector

Now it's time to do some wiring!

Take your power tool casing apart. For my drill I only had to remove a few screws to lift off one side of the drill housing. Once this was done I could insert the top of the old battery casing in order to correctly determine the battery polarity for the wiring.

Take a length of 14ga wire, strip the ends of the wire and solder to the battery contacts inside the power tool. Slide heat shrink tubing over the opposite ends of the wire and solder the wire ends to a XT60 battery connector (most 3S and 4S LiPo battery packs ship with XT60 connectors) and then slide the heat shrink tubing down to protect the wire ends at the connector.

Step 4: Reassembly

Now reassemble your power tool.

Once the tool is reassembled connect the LiPo battery pack. Now plug in the low voltage alarm- there are notations on the alarm as to how to connect it to the battery pack balancing connector. The alarm will beep rather loudly at first and then either three of four green LEDs will light up, showing that each cell in the battery pack is above the cutoff voltage.

As the battery is drained, the LEDs will turn red and an alarm will sound, indicating it is time to charge the battery. Most LiPo cells have a cutoff voltage between 2.8 and 3.0V and the cells can be damaged if they are drained below that level. The alarm is there to notify you when the cells have reached this level. The low voltage alarm will work with 2S to 4S batteries.

Once everything is working properly you can clip the bottom of the battery casing back into the power tool and you're good to go!

Step 5: Finished!

Now experience the joy of Lithium power!

I have several drills that I've converted using this technique and they all work better than they did when they had NiMH batteries.

I really like the old robust Makita stick style drills- they can be found dirt cheap (or even free) and they hold a decent size battery as well. The beauty of these old style drills is you don't even need to take apart the old battery case as the battery just slides right in the grip. The mini Makita stick drill is one my son found for $3 at a recycling center. When he found it it didn't have a battery but I knew we could fix it up as soon as we got home so he bought it and he's been using it ever since for his own projects.


Won't the battery alarm drain the battery over time?

Yes, it most certainly will. I've developed the habit of keeping the batteries unplugged until I'm ready to use my tools. It takes me maybe ten seconds to plug them back in and since the LiPo packs have such a low self discharge rate my tools are always ready to go.

Don't LiPo packs require special chargers/procedures?

They absolutely do. Here's a good guide to understanding LiPo packs and how to care for them- A Guide to Understanding LiPo Batteries. There is more info about LiPo batteries and safety here. If you're not comfortable handling LiPo batteries and going to the extra trouble of maintaining them properly then this instructable probably isn't for you. If they are treated properly they are perfectly safe for every day use, but it's not something I would recommend if you're using tools on a construction site as they're not really practical for that application. I've been using these tools for quite some time now with absolutely no negative side effects.

If you are really worried about an overload condition (motor shorting/stalling, etc.) then you can install an automotive blade type fuse on the positive power lead from the battery connector to the tool (not on the battery pack.) These fuses will increase the load resistance so you will have to do some testing to obtain the right value but it should be below the total current capacity of the battery.

What about LiFePO4 batteries?

Yep- you can use those too. While I used a 2s Li-Ion battery in my son's drill and it works just fine ( I already had this battery pack from a broken RC helicopter that was given to me at home ) LiFePO4 batteries are a better choice. The advantage of these batteries is that they tend to be a bit more durable than LiPo packs but they can be a bit larger so they may not fit inside many power tools. If you can find a pack that fits then great- just be sure to use a pack that either has a built in protection circuit or be sure to use a low voltage cut off alarm. Again, you will need a special charger for these batteries.

Isn't the battery capacity less than the original manufacturer's?

In the case of my 14.4V Makita drill- yes. But I don't really care as I found I'm rarely trying to drive 200+ decking screws from a single battery charge. Since the batteries are so inexpensive I can also afford to keep several packs on hand.

What do I do if I have a tool that has a plug in battery but I don't have the original battery?

In this case you'll have to get creative. Two options are 3d print a suitable battery case or vacuum form one from plastic sheet.

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102 Discussions

I'm facing a similar problem with Harbor Freight's Drill Master 18 volt NiCd batteries. I have a few but one of them will no longer hold a charge. I had read an online review for a new Warrior® 18V tool and the writer said that it could be used on the Drill Master tool, but no, it did not. They are similar not the same. The Warrior battery is actually smaller in size though with the charger built into the battery casing and an 18V AC adapter that just plugs in to charge the battery. Has anyone tried to hack the Warrior® battery into the Drill Master battery housing?


9 months ago

Having seen one of these LiPo batteries explode I would not recommend to use LiPo. LiFePo4 or Li-Ion are a much safer route; but then again maybe not all people drop their tools as often as I do.

The idea is great, but I have concerns about LiPo safety.

1 reply

LiPos are pretty safe when handled correctly. With a small BMS which controls the cell voltage during use and charging, it is no problems with LiPos. I have dealt with LiPos for as long as they have been available on the market. Explosive behaviour might happen under extreme abuse like short circuit, or plug it into the 115V/230V mains, stabbing it with nails an knifes etc.
Explosive behaviour might happen very rarely under seemingly "normal" conditions, but where the control circuits has failed.
LiFePo4 or Li-Ion might be safer due to its metal housings, but much of the same reactive chemicals as LiPos.

1. Que salvada!, yo tengo un taladro inalámbrico, que se me le cayo la batería, y quedó inservible, intentare este proyecto para poder utilizar el Taladro, Foco, sierra circular y sierra sable que utilizan la mísma batería.

Hey thanks for a really cool informative article! The only thing I disagree with is using a lower voltage battery than is recommended for the drill motor. This could draw too much current through the circuit which could in turn overheat the drill and/or damage the circuit. Another thing I'd like to note is that opening the battery case or other plastic cases similar is very much easier if you use a hacksaw with a round blade. Thanks again for the great instructable!

9 replies

Eh? How will it draw more current if the voltage is lower?



Less voltage = less current, it's a resistive load mainly. Not a transformer!

The drill will just run slower and not be as powerful using less current.

I was a distributor for Xtar batteries and have a supply sitting around. In those I have several boxes of 5,000 ma 26650 protected cells. I have some small balance circuit boards about size of two nickles side by side.

(also have an equal number of 4,000 ma unprotected cells to play with)

I have a DeWalt 12v cordless and a DeWalt 12 v right angle cordless sitting useless on my shelf.

Guess what I'm going to do! 3x3.6 v = 14.4 V. The two extra volts should not matter and would give me a bit more power. With the balance charger built in I can just direct plug to about 16-18 vdc to charge the pack.

It's actually not mainly a resistive load. The ohmic resistance of a drill-sized DC motor is quite low. If you've ever used a circular saw ("skill-saw") and stalled it, you may have blown the fuse/breaker and wondered why. With a locked armature, about the only thing limiting the current is that resistance.

No, it's not a transformer, but the inductive component is doing most of the current limiting. Look up variously called "back emf" or "counter emf." This is he voltage generated opposite the polarity of the supply. Under no-load condition, it will be almost as much as the supply, but opposite. That's why the current is lowest then. When the load increases, the "generator" effect diminishes so the difference between the supply and back-emf is greater and the current goes up.

In the USA, if there is a drop in the supply voltage from the electric company, we call it a "brown-out." Air conditioner motors slow down, the cooling fans for the motors slow down, the current through the motor starts climbing, the additional current through the armature and fields creates more heat, and you hope the thermal limiter works before the motor burns up.

Agreed. With motors going slightly over voltage would be better than a not under. Only risk would be if there are electronics controlling the speed and you exceed their max voltage rating.

I believe Max voltage rating is except 0.4 difference since most of transistors have %1 up and down property.

No one builds with components with only a .1% margin for over voltage, and there is no problem with lower voltages set all. Other components, such as capacitors, also have max voltages. With a circuit built for 12V, you'd see commonly see components rated for 20 to 25V, very rarely as low as 15V.
BTW, I'm speaking from college training in electronics and many years in the field.

Just how much leeway you have will vary from one tool to the next.

I have a 14.4v cordless drill with dead NiCad batteries, so I thought I'd try powering it with an 18v lithium pack. The motor works fine at 18 to 20 volts, but the PWM power switch circuit burned out. I replaced it with a switch from another 18v drill with a smaller motor and now it works great.

So if you try a higher voltage, be prepared just in case something in the electronics does burn out.

Ahh, misread the last paragraph about the capacity and was thinking voltage. That's my bad! :D

None of the batteries I used were rated under the factory battery pack voltage for each drill so not sure what you mean by that.

Using a hacksaw blade is definitely better for opening seam welded battery packs than a cutoff wheel- learned that after the first one I converted! The cutoff wheels have a tendency to melt the plastic. I'll update it to show the saw I used on subsequent packs.

Hi switcher, I may be a bit late to answer your problem but try almost any other store :-

Great article also Honus,

I have seen these Instructables previously and whilst very interested I have not signed up. on the strength of this one I have taken the plunge... Although I feel that I am way behind all of you by the way that you are all talking.

I may be sounding stupid to you all but here goes.

The charger for these LiPo batteries would also have to be changed, this I understand.

Firstly, how do you charge these new batteries? Do you dismantle the battery pack to to disconnect the wiring to be able to connect it to the new charger?

Would it not be easier to replace the batteries, leave all the connections to the drill as-is and wire a connector to the casing of original charger (after having removed the charging circuits from it) so that you can charge the battery? That way you can still utilise the charger unit and do less damage to the battery pack which has perfectly good designed connectors that are meant to be dis-connected and re-connected regularly.

I ask this as I fully intend to do this conversion to my cordless which has been sat in my store for a couple of years now (I don't like to throw away anything).

Secondly, I am not familiar with LiPo batteries but it sounds as if these may not be the best, reading between the lines. Were these used just as you said because you had some kicking around? What would be best to re-instate the original speed/torque characteristics of the battery?

Thank you soooo much! I have had an old 14.4V Makita for years--couldn't part with it just because I couldn't replace the two old battery packs. Now I don't have to!

Weight reduction. Another reason to convert NiCad or NiMH to Li-Ion.

More power for less weight.

And costs down to 25% of OEM replacement.

I also add a Balanced Monitor charger circuit to my tool(s) so the charge terminates at 4.2V . In one tool, I wired the multi-connector for monitor/charger externally, and disconnect the Bal/Mon during operation.

I think your use of shrinkwrapped Li-Ion assembly is a good yip; I used the 18650 holders but (rough) tool use caused the cells to jump out of the holders, breaking contact after a mild drop.

On my roto tool (dremel clone) , I think Li-Ion actually has more torque at the start.


1 year ago

Nice one Homus, good clean explenation en well documented. Plan to do the same with my Bosch Blue cordless.

Excellent detailed instructions. For those not ready to make the switch to Li, here's an alternative. I bought an 18v NiCad battery from Harbor Freight and robbed it of the batteries. I was able, with minor modifications, to replace the NiCads in my drill battery pack with these. They work as well as the ones that came with the drill. The best part - with their 20% off coupon I only have about $16 dollars invested in the battery!