Designing Printed Adapters For Power Tool Batteries

Unless you’re particularly fond of having multiple types of batteries and chargers, you’d do well to make sure all your portable power tools are made by the same company. But what do you do if there’s a tool you really need, but your brand of choice doesn’t offer their own version of it? Rather than having to buy into a whole new tool ecosystem, you might be able to design your own battery adapter.

Note the locking tab that’s been printed separately.

As [Chris Chimienti] explains in the video after the break, the first thing you’ve got to do (beyond making sure the voltages match) is take some careful measurements of the connectors on your batteries and tools. His goal was to adapt a Milwaukee M12 battery to Makita CXT tool, so if you happen to have that same combination of hardware you can just use his STLs. Otherwise, you’ll be spending some quality time with a pair of calipers and a notepad.

Once the interfaces have been designed and printed, they are wired together and mounted to opposite ends of the center support column. In theory you’d be done at this point, but as [Chris] points out, there’s a bit more to it than just wiring up the positive and negative terminals. Many tools use thermistors in the batteries for thermal protection purposes, and when the tool doesn’t get a reading from the sensor, it will likely refuse to work.

His solution to the problem is to “hotwire” the thermistor lead on the battery connector with a standard resistor of the appropriate value. This will get the tool spinning, but obviously there’s no more thermal protection. For most homeowner DIY projects this probably won’t cause a problem, but if you’re a pro who’s really pushing their tools to the limit, this project might not be for you.

Of course, this isn’t the first time we’ve seen somebody adapt batteries from different brands to work on their tools. It’s a common enough problem once you start building up a workshop, although you could always avoid it by building all your own tools.

26 thoughts on “Designing Printed Adapters For Power Tool Batteries

  1. Often the thermistor (or other interface to the internal electronics) is only used by the charger and not by the power tool. The tool runs until some undervoltage or overcurrent protection kicks in. Lets hope that all brands have the protection on the same side. Using a tool which expects a protected battery with a battery from a tool where the protection electronics is situated in the tool could lead to a damaged battery.

  2. omg,,, i was looking for a way to do this on Saturday. Having adopted a particular battery / charger brand, where can i buy or print or vacuform or… additional ‘receivers’, the female half of the battery. I can deal with the voltage conversions where required, but really wanted an easy way to source a reliable crisp receiver?

    1. Wow Saturday must have been project day. I’m invested in Rigid tools and was looking for a way to get to 12 volts for ham radio stuff and for my 12v solder iron. Looking a a shoe and a buck converter to do the deed. So this may be a way to do that. In a perfect world the shoe would give me the output on a barrel connector or an Anderson power pole.

      1. Here is a less expensive option:

        Purchase the switch and battery connector here (about $4 each):

        3D print a ‘shoe’ for the connector so it attaches to your Ridgid batter here:

        I’ve modified a few of my existing power tools to accept Ridgid batteries using these parts.

  3. Well for older tools generation it would work, but more recent ones like dewalt .. and others … they communicate with the bms battery board, and get some pins configs too, the battery pack are getting intelligent,
    there’s one brand who calculate the received charge(s) and when a certain count is make, the battery pack is declared defective …….

    the 3 pins : + – and the thermal pin days are almost over.

  4. Well, just ordered the same adapter from China several days ago (thereare cross-platform adaptes for Bosch, Makita, Dewalt, Miluawkee, Ryobi and some chinese brands on their online stores)

    I want to buy Bosch Oscillating multitool and power it from Makita accumulators

  5. Ryobi ONE+ Lithium Ion batteries have their under-volt and thermal protection self contained because they’re designed for use on their old blue tools that predate Ryobi’s first use of Lithium Ion.

    What I need to do is make an adapter for the slide on batteries used by an old 18V Harbor Freight reciprocating saw, to adapt to some super common slide on Li-Ion battery. Maybe even one of HF’s own current generation of slide on Li-Ion batteries.

    I also need to complete my mod project to adapt a set of old Chinese 18V NiCd tools to use Ryobi ONE+ batteries. The main design for early 18V import cordless tools with NiCd batteries had them with two cells in a tower that fit up into the tool, with two side clips on the main bulk if the battery. Ryobi ONE+ is the only big company battery that’s anywhere close to that.

    With many of those tools you can shove a ONE+ in far enough to make contact (how convenient that the cheap imports and ONE+ have almost identical battery contacts) and the tool will work though the battery will sit crooked. One could wrap a velcro strap around to hold the Ryobi battery (if sufficient contact is made) but that’s not a hack, that’s just being lazy.

    Thus the modification required is purely mechanical to the tool’s housing to allow the ONE+ battery to insert, locate correctly and lock in. A bit of plastic may need shaved from the hole in the tool for the ONE+ tower to fit.

  6. Great work, but there’s room for some obvious improvements:
    1. Why not bypass the tool’s thermistor sensing in the adapter instead of opening the tool and soldering in a fixed resistor? Won’t that resistor mess up the sensing of a regular Makita pack?
    2. Couldn’t a resistor or two in the adapter bring the Milwaukee’s 6.8K thermistor enough inline with the Makita’s 10K to satisfy the tool’s controller?
    3. There doesn’t seem to be enough contact area to handle the current. The Makita battery has two double-sided contacts for each battery terminal while he has one single-sided contact for each terminal. Those single one-sided contacts will overheat and burn out.

  7. I am actually kind of surprised that nobody mentioned one of the most obvious uses: transfering the weight of the battery to your belt/backpack/etc. and having a coiled cable that connects the pack(s) to an adapter on your tool. (I would use a magnetic coupling system to prevent… issues.) As you wouldn’t have to deal with the extra weight at the end of your arm, you could have a number of batteries in parallel (or one big custom one) sitting snug on the back of your hips.

    1. You realize you’d want something the thickness of jumper cables to transfer decent amounts of power without radiating it all away as heat and slowing your tool down?

      1. Have You ever used a pneumatic tool? Cable thickness is about the same as what you’re suggesting. I can think of a lot of instances were having a cable linkage to either a tool belt battery pack or a cart based system would be rad. They used to sell small regulated air bottles that strap to your hip what that can power air tools. Only a few specialists use these now, but I could see a belt battery system working similar.

  8. Rechargeable power tool batteries are typically a cluster of single cells.

    For example, the 18v cordless drill battery with a lithium battery will consist of about 4 individual Li-Ion battery cells, since Li-Ion batteries can usually deliver 3.6v-4.2v per cell.

  9. Hi,

    I learned something great from your description. In your content, especially since I found out “Many tools use thermistors in the batteries for thermal protection purposes”

    I have read your content and I understand that you have a lot of knowledge in this regard. I would be very happy if I got a reply to this question. I am waiting for your reply soon.

    Which power tool batteries are interchangeable?


  10. Hi there! At 9:30 the above video talks about different values of the thermistors in various batteries and says that this is why the thermistor needs to be bypassed. I think it is also possible to put e.g. a 22K resistor in parallel with the 10K one inside the battery in order to come to a common value of 6,8K. That way it would be possible to allow the original thermal monitoring to work. Is that right? The question is if we can attach the second thermistor to some accessible poles so that the battery case would not have to be opened. I am not an engineer, just a hobbyist, so if you are an expert, please, share your opinion on this idea. Thanks!

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