Ryobi Zero-Turn Mower SLA to LiFePo4 Conversion - (Updated - Build Complete With Pics!)

I dropped in a 48v 100AH LiFePo4 battery from ampere time. https://www.amazon.com/gp/aw/d/B09BR4JZTT?psc=1&ref=ppx_pop_mob_b_asin_title
It fits fine in the tray and has it’s own BMS built in. I built some spacers to keep it secure in the tray form leftover plastic siding I had.

Is there any reason I can’t just use the ryobi charger that came with the mower? 48v, 13a.

I did order this charger just in case but would rather not rewire the plug if I don’t need to.


I did buy the new display module but haven’t tackled that yet. https://www.amazon.com/gp/aw/d/B088RG27LS?psc=1&ref=ppx_pop_mob_b_asin_title

Trying to keep it as simple as possible. Anything else I should be aware of so I don’t burn my barn down?

You should be fine. It's a little much for the LiFePo4. Actually charges at 56+ I think. But the BMS will cutoff prior. Only problem is that the Ryobi charger will sometimes go into an error state when the BMS kicks it off. That's what I found anyway.

AMDPower said:

You should be fine. It's a little much for the LiFePo4. Actually charges at 56+ I think. But the BMS will cutoff prior. Only problem is that the Ryobi charger will sometimes go into an error state when the BMS kicks it off. That's what I found anyway.

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Thanks and thanks for pioneering the way!

AMDPower said:

You should be fine. It's a little much for the LiFePo4. Actually charges at 56+ I think. But the BMS will cutoff prior. Only problem is that the Ryobi charger will sometimes go into an error state when the BMS kicks it off. That's what I found anyway.

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any issue with the mower not wanting to operate at that high of a voltage? I read something about it not working here: https://forum.toolsinaction.com/topic/11662-ryobi-battery-riding-lawn-mower/page/3/

not sure what the issue could be since some people clearly have made it work

dochoot said:

I dropped in a 48v 100AH LiFePo4 battery from ampere time. https://www.amazon.com/gp/aw/d/B09BR4JZTT?psc=1&ref=ppx_pop_mob_b_asin_title
It fits fine in the tray and has it’s own BMS built in. I built some spacers to keep it secure in the tray form leftover plastic siding I had.

Is there any reason I can’t just use the ryobi charger that came with the mower? 48v, 13a.

I did order this charger just in case but would rather not rewire the plug if I don’t need to.

https://www.amazon.com/gp/aw/d/B09LLV77VW?psc=1&ref=ppx_pop_mob_b_asin_title

I did buy the new display module but haven’t tackled that yet. https://www.amazon.com/gp/aw/d/B088RG27LS?psc=1&ref=ppx_pop_mob_b_asin_title

Trying to keep it as simple as possible. Anything else I should be aware of so I don’t burn my barn down?

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Very interested in your approach and how it's working out for you. I've considered going the same route you did, as it seems to be the most "plug and play option" there is. The cost difference is significant though. It would help a bit if the existing charger was able to be used without issues.

I also want to thank AMDPower, UltrasoundJelly and all others here for sharing their knowledge!

Jakeman said:

Very interested in your approach and how it's working out for you. I've considered going the same route you did, as it seems to be the most "plug and play option" there is. The cost difference is significant though. It would help a bit if the existing charger was able to be used without issues.

I also want to thank AMDPower, UltrasoundJelly and all others here for sharing their knowledge!

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Finished installing everything today, now charging. I did end up splicing the ryobi cord onto the charger I bought. Will test tomorrow and have about 4 acres to mow Saturday, will update then.

Good luck! For what it's worth, I've been using the original Ryobi charger with my LiFePO without issues so far. The key thing is whether you can trust your BMS to cut off the charge beyond a certain individual cell voltage. The Overkill BMS has an app where I can see (and modify) this cutoff voltage. I would imagine the Ampere Time must have this feature, but don't know for sure.
Please let us know how it goes! I just did my first mow of the season, everything good.

Looking forward to the results.

Have my Ryobi ready to go after repainting the underside of the deck with Chassis Saver coating. Will see what the OEM batteries have left in them, but I'm not too optimistic. Have some time to figure out my best option for Lithium as I have 4 other mowers to use if needed. Mowing season hasn't arrived in our neck of the woods yet but with the warm temps predicted, it won't be long.

Was able to mow today. 2.5 acres. 48 degrees F outside. Grass was 5-7 inches, cut down to 3”. Took about 1h 45 mins. 20% battery left. Blades never bogged down, up and down hills easy. Before I replaced my OEM batteries, they were only lasting about 0.5 acres before the blades would stop and I would have to charge. Highly recommend converting. The pre made battery was expensive, but I definitely needed the upgrade and shaved some time off my conversion. My mower is about 2 years old at this point and kept plugged in at all times in my barn. I live in western Washington so mild winters usually.

That's great! Would love to see some photos of the conversion. Did you ever get this much mow time out of it back when the mower was brand new?

dochoot said:

Was able to mow today. 2.5 acres. 48 degrees F outside. Grass was 5-7 inches, cut down to 3”. Took about 1h 45 mins. 20% battery left. Blades never bogged down, up and down hills easy. Before I replaced my OEM batteries, they were only lasting about 0.5 acres before the blades would stop and I would have to charge. Highly recommend converting. The pre made battery was expensive, but I definitely needed the upgrade and shaved some time off my conversion. My mower is about 2 years old at this point and kept plugged in at all times in my barn. I live in western Washington so mild winters usually.

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Nice! Never was able to get more than 1.5 acres with mine, if that. To be fair, my property has many obstacles that slow down the process greatly. I also cut down to 1.5" - 2" and don't let the grass get overgrown. I would be extremely happy with 2 acres to a charge.

When my attached garage was unheated I used a heated battery blanket around the batteries during the few times the garage actually got below freezing. Now that I insulated and installed heat in the garage, that is a non-issue.

Any issues with the new charger?

rio said:

That's great! Would love to see some photos of the conversion. Did you ever get this much mow time out of it back when the mower was brand new?

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when the mower was new, the blades would cut out regularly after about 1.5-1.8 acres and I would have to go home, charge and then finish later. So definitely improved over even when it was new. I should have taken some photos before I put everything back together. I’ll open it up later and take some photos.

Jakeman said:

Nice! Never was able to get more than 1.5 acres with mine, if that. To be fair, my property has many obstacles that slow down the process greatly. I also cut down to 1.5" - 2" and don't let the grass get overgrown. I would be extremely happy with 2 acres to a charge.

When my attached garage was unheated I used a heated battery blanket around the batteries during the few times the garage actually got below freezing. Now that I insulated and installed heat in the garage, that is a non-issue.

Any issues with the new charger?

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New charger is working great! It charges about 10% per hour. Really happy that I made the switch. This is what the mower should have been originally. I would have paid extra for the LiFePo4 batteries.

First, thank you all for this tread! Awesome job you all have done!

Landscaper from Norway here. Will be doing the conversion on Ryobi Z-turn from SLA to a 16s 240AH Lifepo4 setup. Was going to do a 310AH but we got these 230AH(Actual 240AH from 3.65-2.5V) cells from a local supplier that had some B-grade he sold super cheap. Will use a 25A charger so that we can charge in between jobs. Goal is to get 5+ hours out of it + whatever time we can charge when doing other jobs. Will be a test for when we get the 54" that we will have 310AH and a 50A charger on. Need to replace the charging port on that one.

Already gotten the batteries in house, they have been tested, charged and top balanced. Will use a Daly 150A BT BMS and after reading about its performance it seems a shunt is a waste. Any thoughts on the shunt? Will build an acrylic(?) box(Plexiglass in Norwegian).

Have read this whole tread but I'm not quite sure about what to do with the gray/white cable with the small white connector that is attached to the battery. Or the blue one. They both seem to be useless when converting to lifepo4. Except that the blue one needs to be attached to the 48v positive charge(?) so that the charger will not think it is connected to the charger. Is this correct?

Can anyone give an actual average A draw over a time period in different conditions? Like an hour or two in high wet grass or dry short grass. I have seen so many different numbers. From 30-90A an hour but never specifics.

Will be posting pictures and updates from the build.

Finally got the new battery installed! But not quite finished yet. I was nervous that the box wouldn't fit and it is extremely close in height and width. These are the 200 Ah cells I mentioned earlier. Here are some pics.

I had to use a steel box as there wasn't enough room for timber, and couldn't get a sturdy top cover because of the height. But I needed some cover on the top as all the terminals are exposed and it's so easy to drop a tool or wire across. I already managed to get sparks and some smoke when trying to connect up the bus bars! Damn those metal tools! I also had to put in some nylon straps around each pack of 4 cells as it was impossible to lift them out because of the lack of space.

I decided to use a disconnect switch as well as the fuses (2 - one in the +ve line and one in the negative, but only because it was a convenient way to bolt the cables together) and used the shunt for the SoC/amps/volts display.

I'm having some issues with the Daly BMS. It is going open circuit when current rises above 5 amps or so and I have to use the bluetooth app to reset. For some reason it seems to take the discharge limit as milliamps! But I did manage to keep it running and did some trial cuts of heavy wet grass. The shunt monitor showed between 20 amps with no cutters (just driving) up to 105 amps when cutting heavy grass.

There is no room for the battery securing bolt, so I am going to make a clamp to hold the box down at the lip below the BMS.

There are 2 devices that were attached to the old batteries. I think one is the thermistor but what's the other one that is set in resin and has no electrical connection to the battery, even though it is bolted to a terminal - or is this the thermistor? See below:

Kallekanin said:

First, thank you all for this tread! Awesome job you all have done!

Landscaper from Norway here. Will be doing the conversion on Ryobi Z-turn from SLA to a 16s 240AH Lifepo4 setup. Was going to do a 310AH but we got these 230AH(Actual 240AH from 3.65-2.5V) cells from a local supplier that had some B-grade he sold super cheap. Will use a 25A charger so that we can charge in between jobs. Goal is to get 5+ hours out of it + whatever time we can charge when doing other jobs. Will be a test for when we get the 54" that we will have 310AH and a 50A charger on. Need to replace the charging port on that one.

Already gotten the batteries in house, they have been tested, charged and top balanced. Will use a Daly 150A BT BMS and after reading about its performance it seems a shunt is a waste. Any thoughts on the shunt? Will build an acrylic(?) box(Plexiglass in Norwegian).

Have read this whole tread but I'm not quite sure about what to do with the gray/white cable with the small white connector that is attached to the battery. Or the blue one. They both seem to be useless when converting to lifepo4. Except that the blue one needs to be attached to the 48v positive charge(?) so that the charger will not think it is connected to the charger. Is this correct?

Can anyone give an actual average A draw over a time period in different conditions? Like an hour or two in high wet grass or dry short grass. I have seen so many different numbers. From 30-90A an hour but never specifics.

Will be posting pictures and updates from the build.

Click to expand...

I've completed 2 mows with the LiFePO4 battery, and it's a world of difference from the oem batteries. I was finally getting maybe 10 - 15 minutes with the old batteries. You can see on the attached graph the current and voltage during a session. The blades draw more current, with total current peaking near 90 amps when they start to slow down in heavy grass. Also notice that the voltage is very constant, even at maximum load. I'd guess that the lead acid batteries had a lot of voltage droop under load, so much that the mower shut down.
I originally was going to install a separate battery meter w/shunt, but I didn't want to alter the mower during its warranty period. I'm glad I didn't because the android app for the bms does everything and more than the meter. I just use an old 3g phone in the cup holder.
The grey cable that attaches to the battery lug is a temperature sensor used by the charger. I don't think it is used by the mower itself. I think the blue one locks out the mower when the charger is connected.
I got the charger AMDPower got, and it works fine for me. I installed an IEC power entry and just plug the charger in. Of course, for 25 or 50 Amps, you'll need something else.

Thanks AMDPower and all the other members for the research and sharing your work on this effort.

I too have the Ryobi zero turn mower that was in need of new batteries. When my mower was new the original batteries would just make it thru one mowing. Last year I had to recharge them twice to mow the entire lot once. My lot is 2 acres, has some fairly steep hills, and takes about 90 minutes to mow.

I wanted to replace the original batteries with LiFePo4 batteries but didn't know what to use, or how to assemble them. While researching batteries I found your thread and it didn't take long before I was buying the parts. I went with 150ah cells, the Overkill BMS, CAMWAY battery monitor and AIMS charger. Following this thread, it didn't take me but a few days to assemble my battery.

Yesterday I mowed my lot for the first time with the batteries. The batteries started at 99.8% and when I finished they were at 76%. I can probably mow my lot 3x before needing to recharge them.

Thanks again to everyone that has contributed to this thread.

Whoa, this trend continues to blow up!! This is awesome.

@icenov, regarding the arrows in your photo: you're correct. The left arrow points to the thermistor, which you ONLY need if you plan to use the original Ryobi Delta charger (I do, so I kept it connected to the charge port). If you're using a new dedicated LiFePO charger then you can remove the thermistor altogether. The right arrow points to some sort of relay which prevents the mower from turning on when the charger plug is in the charge port. You need to keep both its connectors connected, otherwise you won't have ignition. Alternatively, you can bypass it by connecting the blue wire (the one in the barrel-type connector) to battery positive.

rio said:

Whoa, this trend continues to blow up!! This is awesome.

@icenov, regarding the arrows in your photo: you're correct. The left arrow points to the thermistor, which you ONLY need if you plan to use the original Ryobi Delta charger (I do, so I kept it connected to the charge port). If you're using a new dedicated LiFePO charger then you can remove the thermistor altogether. The right arrow points to some sort of relay which prevents the mower from turning on when the charger plug is in the charge port. You need to keep both its connectors connected, otherwise you won't have ignition. Alternatively, you can bypass it by connecting the blue wire (the one in the barrel-type connector) to battery positive.

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Excellent, thank you.
Also just to comment about the original Pb-acid batteries, we also found the lifetime to be very poor. The hr gauge on the SoC shows 90 hr operation, but the mower had almost become unusable. I just don't think AGM Pb-acid can cope with this type of heavy use. Maybe if you just trimmed a small patch of lawn for 20 mins every other week they might survive, but with solid use the capacity fade is terrible.

Meshdish63 said:

Thanks AMDPower and all the other members for the research and sharing your work on this effort.

I too have the Ryobi zero turn mower that was in need of new batteries. When my mower was new the original batteries would just make it thru one mowing. Last year I had to recharge them twice to mow the entire lot once. My lot is 2 acres, has some fairly steep hills, and takes about 90 minutes to mow.

I wanted to replace the original batteries with LiFePo4 batteries but didn't know what to use, or how to assemble them. While researching batteries I found your thread and it didn't take long before I was buying the parts. I went with 150ah cells, the Overkill BMS, CAMWAY battery monitor and AIMS charger. Following this thread, it didn't take me but a few days to assemble my battery.

Yesterday I mowed my lot for the first time with the batteries. The batteries started at 99.8% and when I finished they were at 76%. I can probably mow my lot 3x before needing to recharge them.

Thanks again to everyone that has contributed to this thread.

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Sounds like you nailed it! Great job!

Could you please tell us where you bought your equip and costs? On the fence between a ready to go 48v, 100ah battery or building one. 150ah is very tempting. Having to order straight from China and the possible problems is pretty scary though!

dochoot said:

New charger is working great! It charges about 10% per hour. Really happy that I made the switch. This is what the mower should have been originally. I would have paid extra for the LiFePo4 batteries.

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Thanks, glad to hear that.

I knew I was taking a chance on the Ryobi's batteries not holding up. I researched and found nothing, at the time, to compare price wise and performance wise. I also would have paid extra for LifePo4. I've spoken to others who bought the Ryobi, thinking it was Lithium powered, without doing proper research.

Jakeman said:

Sounds like you nailed it! Great job!

Could you please tell us where you bought your equip and costs? On the fence between a ready to go 48v, 100ah battery or building one. 150ah is very tempting. Having to order straight from China and the possible problems is pretty scary though!

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Aims charger $275 and Camway battery monitor $46.99 from Amazon.

LiFePo4 cells from Aliexpress $886.16. The store i bought them from had inventory in the USA, got them in about 2 weeks.

16s BMS from Overkill $153

I seriously cannot believe the interwebs sometimes. I started this thread with a question that I assumed was extremely niche but got valuable feedback. After which, I saw multiple people do similar builds (and some a lot better!) for the mower that I didn't think anybody else even had. Crazy. Love it! Also...did a full mow on 1.25 acres after my backyard finally dried out this season. 66% left! Vroom!

Meshdish63 said:

Aims charger $275 and Camway battery monitor $46.99 from Amazon.

LiFePo4 cells from Aliexpress $886.16. The store i bought them from had inventory in the USA, got them in about 2 weeks.

16s BMS from Overkill $153

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Thanks for that! USA inventory would be nice. All that sounds pretty reasonable.

AMDPower said:

I seriously cannot believe the interwebs sometimes. I started this thread with a question that I assumed was extremely niche but got valuable feedback. After which, I saw multiple people do similar builds (and some a lot better!) for the mower that I didn't think anybody else even had. Crazy. Love it! Also...did a full mow on 1.25 acres after my backyard finally dried out this season. 66% left! Vroom!

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Look what you started...Thanks!

Narrowing down my options, thanks to all the info here.