Ryobi 18V One+ Battery to Greenworks 40V Mower Adapter

6/21/25
After using the P197 batteries for a few mows and inserting them and removing them, they developed little nicks in the retaining clips; the part you squeeze on the battery to remove it, in particular the sharp wedge area that actually grips/locks the battery in place. Those nicks made them wider by a 'very' little bit. This resulted in not being able to remove the battery very easily; very hard actually. I measured the distance between those two opposing retainer clips and they are manufactured wider than the older batteries. What I did is took an Xacto knife and shaved off the edge of both of those clips on the battery so they slide in and out easily.
I also made a few more modifications to the RyobiBatteryReceiver.stl so going forward, anyone that makes this 'thing' will not have any problems.

In short, the newer P197 batteries are not the same size as the older batteries, there are very slight size increases that affect any after market "thing" designed with close tolerances to use these batteries, ie, they'll be hard to remove or get stuck.
I fixed all that with this new upload of the STL and STEP file.

6/15/25
The P197 Batteries must be a bit bigger than all the varieties of older batteries I have. After mowing with the P197's in the hot weather they were hard to pull out and it wasn't due to the contacts being too tight, I think the top shaft of the battery is slightly bigger than all the older batteries. The older batts insert and remove really easy, but not these newer ones.

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6/7/25 UPDATE

I modified the RyobiBatteryReceiver STL and uploaded it to the files section. This fixes the issue described in the 6/6/25 Note.
I also uploaded a new version of the STEP file which contains all components.
The batteries slide in and out very easy now.

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6/6/25 IMPORTANT NOTE:

I got some new Ryobi batteries and they fit tighter when pushed all the way in. I'm sure it is due to the new terminal design on the batteries; they have a sort of rough texture to them whereas the older batteries are smooth.
I'm very sure what is happening is the terminals inside this adapter are getting pushed farther apart and there isn't enough space for them to spread apart; they hit the wall instead of spreading out. It takes some pulling and swearing to get the newer batteries out.
For those of you that can use the step file to modify it, make a little extrusion next to the terminals to give them more room to expand when they spread apart when the battery is inserted.
I will be working on this mod when I get a chance and will post it when it's ready.

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Summary

This adapter will allow you to use two Ryobi 18V batteries in a Greenworks 40V Mower

There's no need to remove the battery cover from the lawnmower, I removed it during the design of this thing to make it easier to measure, test fit, etc.

This is fairly easy to build, I'm going to try to be very detailed so don't be intimidated by the amount of instructions and text that follows. The only hard part will be soldering the big connections if you don't know how to solder. Soldering the small parts is basic, easy, soldering.

I've been wanting to design this for a while now. I had an original Greenworks 2AH battery go bad and that triggered me to make this. I have a bunch of Ryobi 4AH One+ 18V batteries and didn't want to have to pay the Greenworks price for a new battery. The Ryobi batteries, for me, have been top notch and have lasted years (I've had two of the older 2AH black batteries go bad, they were really old). During the design of this adapter and looking at the "bad" Greenworks battery I discovered what was wrong with the Greenworks battery and it was an easy mechanical fix. More on this later.

This adapter should fit all Greenworks 40V mowers with the side-by-side battery compartments as long as they are 10cm apart measuring from an identical location in each compartment. For instance, the right edges of the battery guides, etc.

The photos at the end show my jury-rigged test setup. It's all you really need to make this work. The first time I mowed I just had that test setup and two Ryobi batteries bouncing around in the mower. It worked great! I got 22 minutes out of two older Ryobi batteries and I was loading the mower down, big time, to where it was in high current mode the entire time. I wanted to be sure that all the connections could handle the current. I had the mower lowered all the way down so I could scalp crabgrass. When the batteries shutoff I checked all the connections and they were barely warm, the batteries themselves were warmer.

Since completing the adapter I've mowed twice so far and got 37 minutes both times with the same older batteries. One battery is first charge 2014 and the other 2020. The mower went into high current mode maybe 10 times. Your mileage may vary.
UPDATE: I mowed again while also scalping some crabgrass, got just over 23 minutes with the same older batteries. I think the testing phase is over, this adapter works great.

UPDATE 6/7/25: I used two P197 4AH batteries I purchased in 2020 that have been on the shelf since purchase. First charge of both batteries and I got over 42 minutes! The mower didn't go into high-current mode much during this mow. I also used two 1.5AH batteries (older P189 "new 2020" batts, first charge) and got 12 minutes, not much high-current mode while mowing with these either.

Parts you will need:
LM2596 DC to DC Buck Converter 3.0-40V https://a.co/d/0aGjRri7
Two Ryobi 30001044 replacement terminals ( https://www.smallenginesprodealer.com/part-ryobi-300001044/)
1x Arduino pro micro 5 volts / 16 MHz
5x automotive BX2091C fuse terminal connector https://www.amazon.com/dp/B07BFRRXXL?psc=1&ref=ppx_yo2ov_dt_b_product_details
You will need to program this code onto your Arduino to talk to machine in order to convince it to work: https://github.com/softwarecrash/OmegaFaker
Turnigy High Quality 14AWG Silicone Wire 1m (Red) https://hobbyking.com/en_us/turnigy-high-quality-14awg-silicone-wire-1m-red.html
Turnigy High Quality 14AWG Silicone Wire 1m (Black) https://hobbyking.com/en_us/turnigy-high-quality-14awg-silicone-wire-1m-black.html
I had the above Turnigy wire from a long ago order. Anything similar that is 'very' flexible will work. It needs to be snaked through the channel between batteries. It was pretty easy for me to do it with the Turnigy wire.
Other flexible hook-up wire about 26 - 24 gauge with silicone insulation, this is for the connections to the PC boards. If the wire is too stiff it may break from the vibrations from the mower. This is the wire I used which I already had: https://www.amazon.com/gp/product/B07G2LRX68/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

Files you will need to print:
1 - Connection box
2 - Battery Interface covers
2 - Battery Terminal Interface
1 - Terminal Cover, this ensures that the terminals stay pressed into the slots
2 - Ryobi Battery Receivers
2 - Ryobi Battery Power Clip Mounts
OPTIONAL:
2 - Connection box covers, I don't use them right now because I'm still in testing phase. They're really not needed but they look good installed
2 - Retaining clips, I don't use these, the electrical connections hold so tight these aren't needed

Be sure to review all the photos for how the 3D printed parts go together and how the components are soldered together.

After you have all the parts printed, the BatteryInterfaceCover and BatteryTerminalInterface need to be glued together. The two parts should snap together easily, make sure they snap together "completely", all the way around before putting super glue on the parts. Snap them together and take apart several times to be sure you know they are going to fit because once you put super glue along the edges and they don't snap together correctly they might not be able to be taken apart again to do it over.

The ProMicro_Mount is meant to be glued in place after the Arduino Pro Micro is programmed, wired up, and snapped into the mount.

The step down voltage converter is to be adjusted to 5 Volts, wired up, and then put in place over the two built in bosses under the cover. Those bosses are then melted down to hold the converter in place. One of the photos shows where I used a lighter to heat up a screw head and pressed it against the bosses to melt them against the circuit board.

Solder all the connections together per the photos.

The Arduino Pro Micro and the step down voltage regulator fit into the Battery Terminal Interface part perfectly with no room to spare, it's a tight but perfect fit.

Note that the BatteryTerminalInterface part takes two stacked fuse terminals at the end locations. This is to ensure good electrical contact. Bend the "wings" on the first terminal (no wires get soldered to this one) and insert it upside down, then the terminal with the big and little wire soldered in go on top of that terminal right-side up. The two middle terminal slots only take one terminal and only one of those is used for the data line, the other one can be left empty. You don't need any terminals on the BatteryTerminalInterface side where the spare battery normally goes, if you do put terminals in this side it will just make it harder to remove the assembly from the mower.

Snap the TerminalCover over top of the installed terminals. This part is meant to be glued in place but I haven't glued mine in yet, it snapped in pretty firmly.

As stated earlier, soldering the Ryobi battery terminals may be a challenge for someone not experienced at soldering. For these connections, use an 800 degree tip or turn your soldering iron to 800 degrees. Also use FLUX on all connections, especially these large ones. Flux makes the solder flow much quicker so you don't have to hold heat on them too long. Be sure all large wire solder joints are good joints because they will be carrying a lot of current.

I uploaded a picture of what was causing my fairly new Greenworks battery to play dead after only a few minutes of mowing. While designing this 'thing' I was looking at the Greenworks battery and noticed that one of the terminals was spread apart. This was causing poor contact when inserted into the mower. I took the battery apart and found that the assembly of the battery was a bit sloppy and that terminal was pushing up against the top plastic holding it open. I trimmed the plastic with an X-acto knife and now the terminal springs back into the closed position. You can see in the photo where the plastic is trimmed away a little bit on the end terminal. That fixed it. The terminal board in the battery is soldered on really crappy and the terminals aren't centered in the slots as well as touching the top plastic.