Introduction: Convert Old Cordless Tools to Lithium Power

Picture of Convert Old Cordless Tools to Lithium Power

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

Picture of 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

Picture of 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

Picture of 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

Picture of 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!

Picture of 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.

FAQs

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.

Comments

switcher (author)2016-11-06

I could use a new wire stripper so I clicked on your link. The USA Amazon site wants wants about $15. As I am in the UK I tried the UK Amazon site. If you like a good laugh, click this link:

https://www.amazon.co.uk/gp/product/B005GBJ84W/ref...

I'll probably try something else!

DarranP1 (author)switcher2017-09-10

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

https://www.toolstation.com/shop/Hand+Tools/d10/El...

http://www.screwfix.com/c/tools/pliers-cutters/cat...

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?

mkrobert (author)2017-08-01

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!

TheRadMan (author)2017-08-01

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.

Filx (author)2017-07-31

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

TDJ2591 (author)2017-07-31

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!

Sandre01 (author)2017-07-31

Excellent ,good jobs

JamesK185 (author)2016-08-13

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!

Fusesvc (author)JamesK1852016-08-14

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

V=IR

I=V/R

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.

UncleEd (author)Fusesvc2017-07-30

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.

Tanzer26 (author)JamesK1852016-08-13

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.

signOnthe (author)Tanzer262016-08-14

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

Tanzer26 (author)signOnthe2016-08-14

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.

grunthos (author)Tanzer262016-11-24

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.

JamesK185 (author)Tanzer262016-08-13

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

Honus (author)JamesK1852016-08-13

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.

HippieC (author)2017-03-05

i repair batteries for a living and like these DIY tutorials. But there are some issues that i dont agree with in this tutorial:

*If the replacement battery cost more then it usually has far better capacity the your old one.

*If you change the chemistry you must also change the charger which is another €10-20.

*There is good chance the voltage is to low or too high if you change to lithium so it can destroy the power tool.

* If you need to repair a NiCD/NIMH/Ni-ZN battery be sure to buy NIMH cells (usually 4/5 SUB C sizes with soldering tabs). Lipo is not recommended for DIY packs since they can overheat and burn if mistreated! Lipo packs also need to have BMS which some hobbypacks like these dont always have!

Safety first!

KristianR14 made it! (author)2017-01-19

Converted my old Wuerth power tool to LiPo, as the original bateries had only 7V fully charged. the batery case is pretty big, so enough space for all components. very easy conversion and now it works perfectly

sonic_1 (author)2016-08-13

One needs some knowledge with LI batteries. I'm sure most of you know about the problems with the Hoover boards. Even Boeing had problems with the Dream Liner batteries. I gave up on battery power tools, just use the good old fashioned AC types. No problems with charging, discharging etc. It is rare when I need a power tool that I can't get to plug into an AC outlet. For that, I have a 1 KW inverter in my Prius

heli58 (author)sonic_12016-08-14

" I gave up on battery power tools," "in my Prius" irony much? ;)

Pdwight (author)heli582016-12-27

Owned

Gartholameau (author)heli582016-08-14

good eye heli58 :-)

how do you have it connected to the prius. into that little 12v battery?car will not start if that battery is drained.

Of course the engine needs to be on!
I used to it to keep power on in my house for 3 days when Sandy hit. Used only 6 gallons of gas. With the Prius, the engine only runs when the HV battery is discharged, so it is very efficient for low duty cycle applications.

signOnthe (author)sonic_12016-08-14

Note for Info: DreamLine problem was Li-Ion, not LiPo.

rbormann (author)2016-12-25

Hi. Some welded cases are sensible to sharp blows applied right on the weld line and you can open them with a little hard work. You avoid losing material and it opens clean so you can just glue it back almost invisibly. Try with wall warts before you go real. Best regards.

RobertO139 (author)2016-12-19

I have a DeWalt 18v drill and I would like to do this conversion. I searched Hobby King and decided I would need a 3 cell LiPo and a 2 cell LiPo. I am total ignorant about these batteries and would like to know how to connect the two packs to get the 18.5 volts and can they be charged together?

Honus (author)RobertO1392016-12-19

What you want is a single 5s (5 cell) battery. A 5s battery will be rated at 18.5V. You would not be able to balance charge two individual 3s and 2s packs as single battery.

GurubandhuK (author)2016-12-04

I do not know that much about electrical things. I have a Ryobi NiCad charger a and batteries and want to change it to a Lithium system. Neither works to my knowledge. Isn't there a battery monitor in the NeCad batteries already so I would not need to get new ones? I looked on Hobby King's website but did not see any 18 V battery packs. Where else could I get some? Can I use the old charger for these batteries or do I need to get a new one? Thanks

Honus (author)GurubandhuK2016-12-04

You cannot use a NiCad charger to charge Lithium batteries. Lithium batteries are very particular about charging rates and cell balancing so you need a charger specifically designed to charge Lithium batteries. The closest LiPo battery you can get is a 5S, which is rated at 18.5V.

zappenfusen (author)2016-09-20

The electronics in my Makita drills and impact driver have kept me from attempting a DIY solution. This sounds great for older drills though. I've considered the cheap packs available but bite the bullet and replace with Makita originals. They last for years though thank goodness. I have other devices that I may go this route with. Thanks for all the info you've provided and the comments were an interesting addition.

zapp

TCSC47 (author)2016-08-28

Great idea. I have a couple of old drills that I will convert. They have Ni-Cd cells which did not last very long. Also the big trouble of Ni-Cd is that if you recharge them before they are completely discharged, they have a "memory" effect that effectively reduces their capacity. The only way to always have drills ready to work was to have two sets of batteries. (You might have said this, but I scan read your article - sorry!)

My early Ni-MH did suffer from discharging on the shelf, but my more modern ones keep their charge much better and as I've got a pile of cheap AA of 2000mAh (Chinese, I'm afraid) I'll see how I get on with these. I have an imax B6AC cheap charger which works quite well.

dawp (author)2016-08-23

That sounds like a great idea. In reading the comments i particularly liked the corded to 12 V lead acid as the most expedient. I converted an old 19.2 V Coleman Powermaster electric drill the quick and easy way:

WARNING: do not attempt to recharge this kluge. When the drill no longer has power replace the AA batteries.

1 opened the battery case (six screws) and removed the NiCad battery pack.

2 found i could fit three Radio Shack four AA adapters into the case.

3 wired them in series and connected them to the battery tool connections.

4.bought enough packs of Lithium Energizer batteries to get 12 AA cells. (around $30.00). 12 x 1.5 = 18.6V (note the original batteries are 1.2V and there are 12 of them) The slightly lower voltage doesn't appear to affect performance.

5. inserted them into the AA adapters then closed up the case.

6. plugged the case into the drill in the usual way.

I do not use the drill very often and it is mainly light duty stuff. I found the original NiCad (or maybe they were NiMH) died over time even when regularly recharged and the drill was never usable when needed. I did this over a year ago and the drill is still ready.

As stated in the beginning I have heard that attempting to recharge non-rechargeable lithium batteries is dangerous.. I don't intend to try it just to see what happens.

I have a Black an Decker weed whacker with a similar problem. Both 19.2 V battery packs i got with it have died. I would do the corded 12V and 6V in series trick with it. Maybe it could take 24 volts (two 12V in series) but why risk burning up a $99,00 device. Note a couple of hi powr 3V zeners in the string might be acceptable.

Regards: Davud

I

MFFergison (author)2016-08-17

Very cool , i am going to try it on my dewalt drill / driver. Thanks

Honus (author)MFFergison2016-08-20

Happy to help! If you have any questions when you get into it just let me know!

colins10 (author)2016-08-20

This is a superb project,I have purchased several batteries and a charger and intend to modify and breath some new life into several old drills/electric screwdrivers.

Honus (author)colins102016-08-20

Cool- let me know how it goes!

ace66756 (author)2016-08-13

Fred, forgive me if I am wrong, but to me it seems as if you are a farily young fast speed reader. Otherwise, you would know that most of these tools were around before Lipo batteries was being massed produced, and possibiy before you was even born. Also since you completely skimmed over it, the aurthor posted a hyperlink in hopes that anyone that does not understand the proper care and maintenance they could easily find the information on how too. This is as close to a professonal fix that anyone could do without owning production line. And for your information I am an engineer. I love to get on here and see some of the ingunity some people possess. There are people from all walks of life on this site, and if you think this is dangerous, I would leave this site forever. I have seen a few items that have just out right scared the crap out of me. However, I did not leave any negitive feedback, and in certian cirumimstances offered some tips wheather they was towards safety or to improve thier idea. And please forgive my spelling since i am on my phone and only sat down to take a short break.

geezerbeast (author)ace667562016-08-14

not just spelling but grammar and punctuation also!

ygoloeht (author)geezerbeast2016-08-15

You could have capitalized before you criticized..

geezerbeast (author)ygoloeht2016-08-16

Yes I could have, except that I was using the voice recognition on an iPad, so you can blame it. I WAS guilty of not proofreading before I posted. How many lashes with a wet noodle should I suffer for that offense?

ygoloeht (author)geezerbeast2016-08-17

I did not intend any penalty nor mean to infer an offense. I apologize to you. I am also sorry that the first comment I've made to Instructables was to correct you instead of contributing. I apologize to Honus and Instructables also.

Honus (author)ygoloeht2016-08-17

No need to apologize to me! :)

Tanzer26 (author)2016-08-14

Motors are not a truly resistave load, rather they are an inductive load. One of the major reasons for electric motors failing, is heat due to increase current during voltage sags. Put an ammeter on a ,motor and drop the voltage. Or increase the load on the motor. Thus the reason we track of over current protection being important for LIon batteries.

FredM13 (author)2016-08-13

Wow, with all the know how you posess, I cannot believe you suggest this as a solution to a failed tool battery. Tool engineers go to great lengths to offer the best batteries to do the work. There is more involved than voltage. Yes,your idea will work the tool, but I seriously doubt the performance of your fix (i.e. Power,Runtime,SAFTEY,) Not to mention time spent and costs ,battery & charger. Fact is, the most expensive component of a high end cordless tool kit are the batteries. Once expired, there are after market choices, rebuilders, & in your case instructions and replacement cells available to use the expired case to make a relplacement battery better than the original! You already have the tools & skill set and you can use the original charger. I commend your ingenuity, but with all the time tested options out there I wouldn't go there.

Honus (author)FredM132016-08-13

Of course there is more involved than just voltage- internal resistance, discharge rates, proper charging procedures, etc. The reality is that any battery of specific voltage and discharge capacity can power a specific motor of a power tool. Safety is a concern when you don't use a battery properly with regard to its chemistry and design specification.

Many of the early Lithium power tools were probably less properly engineered than this as some manufacturers didn't bother to balance charge battery packs- some of them were series charged so when one cell in the pack went south the entire pack had to be replaced. Not balance charging Lithium multi cell packs is a real no no. Tool engineers are human and they make mistakes too, especially when they are cost constrained or when management won't let them do something the right way. Good, fast, cheap- pick two. Many engineers don't have the luxury of that old adage due to the constraints of mass production.

As for time and cost- time wasn't a big factor as this was very quick and easy to do. As for cost all I had to buy were a few connectors and one 4S battery pack- I already owned everything else. I did explore many options for battery replacement and this is what worked best for me. It may not be the end all, be all solution but again- it works well for me. Your mileage may vary depending on how you use your tools and what resources you have available to you.

Using these batteries is no different or less safe than flying multi cell RC aircraft. As I stated, if you're not comfortable with the care and handling of multi cell LiPo batteries then don't do it.

FredM13 (author)Honus2016-08-14

My "discomfort" is based with the effort/reward and all the hoops. As previously stated OEM batteries are the most expensive component in a tool and highly engineered. I've owned cordless tools since before the 9.6v (stick as you call it) & currently enjoy 12v,18v Bosch, & 28v Milwaukee Li-on tools. My too use is extensive so I don't have the patience or the time to play with a lipo substitution as you suggest . I totally understand if your limiting the use of the tool with battery limitations in mind it will work, just not for me. The aftermarket availability of the batteries your replacing are a much better solution IMO. If you Magiver a way to hack a modern Bosch or Milwaukee Lion cell I'll be more receptive as the list on a M28 is $180.

Honus (author)FredM132016-08-14

Most of those super cheap replacement packs are just that- super cheap. They usually use pretty poor quality cells in those packs. If I was going to rebuild my packs with NiCD cells then I'd use good quality Sanyo cells or pay the money for a good quality pack.

Milwaukee and Bosch make wonderful tools and I own several tools from both manufacturers. If I was going to buy a new Lithium drill I'd go Milwaukee for sure- their new drills are really nice.

You can have my Bosch worm drive saw when you can pry it out of my cold dead hands. :)

lpxav (author)2016-08-13

Nice job I am doing slightly different as I am 3D printing the battery for my makita and I use recycled 18650 battery. it is more stable ;) and easy to charge too.

FredM13 (author)lpxav2016-08-14

Great idea for the 9.6v hack. Much less choreography????

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