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

[Hedges]

AGM may last several hundred 50% deep cycles. Many people report a couple years for electric mowers, but perhaps a good battery could go 5 to 10 years if properly treated?
Do not discharge beyond 70%, maybe 80% (see data sheet, technical manual for your battery.) usable Wh over lifetime decrease at greater DoD, more steeply if used to 100% DoD. If necessary, mow in two 1 acre runs.
Fully recharge immediately after use. Double check that voltage reached is what battery wants, that charger isn't inappropriate. Try to store in cool location.

 

[Sracer42]

I just snagged a ZT480ex from a local outlet store, factory reconditioned, for $2k. Had 8 hours on it, comes with a 1 year warranty and 30 day return policy, I think it was a pretty decent deal. I know a little about LFP batteries from a small solar setup I built. Immediately thought I could shove one in this thing when the SLA batteries die. Going to bookmark this thread, I'm almost excited for them to die to try and retro fit it! Anyone have any experience how long the stock batteries last? Guessing 2-3 years before it gets noticeable? I'm mowing a little less than 2 acres, probably around 20 times a year. I was reluctant to get it with lead acid batteries and some unfavorable reviews regarding it's longevity, but figured I would give it a shot. I'm already exhausted dealing with my old Cub Cadet's deck problems, worst case I have 2 half working mowers in a few years.

I was figuring 2-3 years. Others have reported longer. Either way - great deal!
Even figuring LiFePo replacement you will come out way ahead on that deal compared to anything new.

 

[Vigo]

I would take a wild guess that a huge chunk of peoples' problems with lead acid mowers is the same as the problems people typically have with other small-engine lawncare equipment.. poor storage conditions/practices.

For a lead-acid mower it's mostly going to come down to charging practices. Lead-acid don't like to be left in a discharged state, which not only means recharging after use but hopefully recharging in a period of less than days. If they sell these things with a tiny crappy single stage charger and claim '2 acres mowing time' because the thing shuts down at 10.0v... then yeah i wouldn't be surprised if people are killing these things running them down to 10 volts and then trickle charging them back up only to float voltage over the course of 2-3 days. Admittedly, i haven't looked into it. But if one was conservative on depth of discharge, and then charged the batteries back up fairly rapidly with a smart enough charger that could also maintain the battery properly in storage, they should last several years.

 

[chazman113]

AGM may last several hundred 50% deep cycles. Many people report a couple years for electric mowers, but perhaps a good battery could go 5 to 10 years if properly treated?
Do not discharge beyond 70%, maybe 80% (see data sheet, technical manual for your battery.) usable Wh over lifetime decrease at greater DoD, more steeply if used to 100% DoD. If necessary, mow in two 1 acre runs.
Fully recharge immediately after use. Double check that voltage reached is what battery wants, that charger isn't inappropriate. Try to store in cool location.

So there is a lot of talk of AGM batteries with these mowers but as far as I can tell, my batteries are just SLA. I guess older models came with AGM? It says my replacement part is LPC12-100T11. As far as I know, the Depp Cycle SLA's don't have the DoD vs Lifespan problem quite as much as the AGM, which for me will be better since I'm pushing the mower's limits.

Actually going to have a chance to mow with it today so I'll see how much capacity it has! But yea, I have a cozy shed for it with power so I can leave it in a relatively stable environment and charge it immediately.

 

[Hedges]

There are sealed FLA batteries with catalytic recombining of H2 and O2, typically automotive starting batteries.
SLA normally means VRLA AGM or Gel Cell. Supposedly Gel Cell is good too, if properly charged, but sold as drop-in replacements in the U.S. they failed quickly and got a bad rap. My Rigid cordless drill has "D" size Gel Cell. My PV system has SunXtender AGM.

The following calls out "Absorbed Glass Mat"

Amazon.com: Leoch LPC12-100 12V 100Ah Wheelchair Battery - This is an AJC Brand Replacement : Health & Household

Amazon.com: Leoch LPC12-100 12V 100Ah Wheelchair Battery - This is an AJC Brand Replacement : Health & Household

www.amazon.com

I suggest not pushing the battery's limits, only do mowing in one session if no more than 70%, possibly 80% DoD. As capacity is lost over time, even that would push toward 100%, so not good. So if over 60% initially, just mow half the lawn one day, half the next. Immediately recharge to full. Confirm voltage achieved and absorption time obeys battery specs.

It could be the batteries will give long life with proper DoD, recharging, and temperature.

Another brand same battery claims 650, 50% cycles, 300, 100% cycles.
But I would rather avoid that.

https://www.leoch.us/pdf/reserve-power/agm-vrla/lpc-deep-cycle/LPC12-100.pdf

My cordless drill, I use occasionally over hours or months until it doesn't run, then recharge. Haven't kept track of cycles, likely not hundreds.

 

[BrianDS]

Figured I'd drop my story here, too. After 3 years and about 95 hrs on the clock mowing less than 1/2 acre, the original batteries needed to be replaced. All this year it was taking 2 charges to finish the lawn. Then a couple weeks ago I couldn't even get it to run 10 minutes. Drive motor would drop out after only a few minutes of running on a full charge. "5 beeps". I went through diagnostics with a Ryobi tech to make sure there wasn't some other problem (motor drive circuit, etc) and based on the significant voltage drop when running he recommended battery replacement.
While I was waiting on replacements, I added a push button for the original volt meter to allow monitoring the voltage more closely. It tracked pretty well with my fluke on the charge port. Why was this not standard?
I wanted to go with a 48V DIY LiFePO4 pack, but needed to get it back up and running so I went with 4 drop in 12V 75ah LiFePO4 that I bought off ebay. I was a little nervous to "reduce" to 50ah but then found these 75ah that are rated for series installation for close to what the OEM replacements were going to run and I received all four in a week. I charged them individually to the same voltage (within 0.005v) with my Noco charger and dropped them into the battery tray just like the originals. I wired them up with the original wiring and also included individual leads to allow independent charging (the manufacturer recommends every 4th cycle). After a full double mow due to the excessive height from the missed week, the voltage is still above nominal.

Next step is to install Qwork current monitor to keep a better eye on the depth of discharge and to watch during the initial charges until I am comfortable with it.

Need to do a little more research to decide how to approach charging since I plan to charge only before use instead of always charging as with the original batteries.

I was considering hacking these open over the off season and dropping on a 48v BMS onto the 16 cells just to make it even easier to manage, but that will likely be pretty far down the list. The performance seems so much better than that I probably won't get around to it for a few years.

If there are any questions, let me know.

I appreciate all of the great content here. It was the best research I could find as I was contemplating the best approach to solving Ryobi's engineering failure.

 

[Sracer42]

Figured I'd drop my story here, too. After 3 years and about 95 hrs on the clock mowing less than 1/2 acre, the original batteries needed to be replaced. All this year it was taking 2 charges to finish the lawn. Then a couple weeks ago I couldn't even get it to run 10 minutes. Drive motor would drop out after only a few minutes of running on a full charge. "5 beeps". I went through diagnostics with a Ryobi tech to make sure there wasn't some other problem (motor drive circuit, etc) and based on the significant voltage drop when running he recommended battery replacement.
While I was waiting on replacements, I added a push button for the original volt meter to allow monitoring the voltage more closely. It tracked pretty well with my fluke on the charge port. Why was this not standard?
I wanted to go with a 48V DIY LiFePO4 pack, but needed to get it back up and running so I went with 4 drop in 12V 75ah LiFePO4 that I bought off ebay. I was a little nervous to "reduce" to 50ah but then found these 75ah that are rated for series installation for close to what the OEM replacements were going to run and I received all four in a week. I charged them individually to the same voltage (within 0.005v) with my Noco charger and dropped them into the battery tray just like the originals. I wired them up with the original wiring and also included individual leads to allow independent charging (the manufacturer recommends every 4th cycle). After a full double mow due to the excessive height from the missed week, the voltage is still above nominal.

Next step is to install Qwork current monitor to keep a better eye on the depth of discharge and to watch during the initial charges until I am comfortable with it.

Need to do a little more research to decide how to approach charging since I plan to charge only before use instead of always charging as with the original batteries.

I was considering hacking these open over the off season and dropping on a 48v BMS onto the 16 cells just to make it even easier to manage, but that will likely be pretty far down the list. The performance seems so much better than that I probably won't get around to it for a few years.

If there are any questions, let me know.

I appreciate all of the great content here. It was the best research I could find as I was contemplating the best approach to solving Ryobi's engineering failure.

Which model mower?

 

[BrianDS]

Which model mower?

38" RY48110

 

[Kavalliero]

I have the RY48ZTR100 mower that I started using in July 2020. I got to about May 2022 before I started seeing serious battery performance loss. I have a little under 3/4 acre lot with about 1/2 acre of mowable lawn. I live in Orlando, FL and cutting bermuda grass which is generally pretty tough on mowers. The unit is stored and charged in an outside shed which in the summer can peak up to probably around 105-110F. The lawn would generally be mowed at least once or twice a week. I used to be able to mow the entire lawn without stopping once per week. Around May/June this year I was running out of charge to complete the whole lawn without stopping to recharge. If I mowed 2/week so that there was less work for the blades I found could just barely complete a full mow before the charge indicator read to 10%. That is when I started looking into battery reconditioning, replacement, and then to conversion to lithium.

I know the SLA batteries were strained but it is always hard to say what the actual charge state is with the stock battery meter. Like many people with these mowers I have had issues with the stock meter almost from the very beginning where even after leaving on the charger all the time it would only show 70% when you turned it on from "full charge". From there it would read discharged to about 40% after the mow. Over time it would go from 70% showing at full charge and suddenly drop to 20% and then later 10%. However, I could turn it off and come back 10 min later and the meter would be back to 40%. The same situation would happen if I was at 70%, I could turn it off and come back and it may show 90% or 100% when I turned it back on. So it is really unclear what the state of charge is but the end result is still the same in mowing.

From a SLA battery perspective in cars in Florida due to the heat and humidity you usually only get at most about 3-5 years out of them. However, with this Ryobi setup it seems like 2-3 years is pretty typical depending on your charging environment and load conditions. Like pretty much everyone here I don't see the reason in investing in more SLA vs swapping in for lithium.

I ran into an issue with my conversion after trying to "refresh" my SLA batteries with a different charger that shorted out my charge port due to its EZGO charging plug having reversed pos and neg wiring. Then I had issues getting the proper charge port from Ryobi due to a longterm backorder. I didn't know if I fried any of the other electronics, but I tried to use a charge port from one of the other Ryobi 48v riding mowers to see if that fixed my problem since those parts were in stock. The unavailable port for the RY48ZTR100 is part HM-996515001. The in stock port from the other 48v riding models is HM-996207001. Note that I still have not received the official part and charger from Ryobi for my particular mower...still on longterm backorder.

After getting the new HM-996207001 port I discovered it is basically the same but it does have a different internal mold inside the receptacle that I had to modify (cut out with snips) so that I could insert and use with my stock charger. Once I got it all hooked up the mower was able to charge again and turn on without issues. So this is a good alternative to anyone that has issues with their charge port and/or charge lockout circuit. Since this charge port is really just a custom mold of a Delta-Q compatible tri-plug EZGO golf/club-cart charger the cheaper route would be to purchase just an EZGO charge port which appears to have the same lockout circuit as the Ryobi. The molding in the port may need to be modified to accept a charge handle. Also and most of the golf/club EZGO charge ports use ring connectors for the pos/neg wiring, so you would need to modify (splice or replace) the connector to work with the existing Ryobi connector.

Be advised that the main problem I ran into in installing the new port (and opening the rear panels to access the batteries) were the clips and screws used to hold everything together. On my mower Ryobi went a bit crazy using threadlock they applied to the screws. The torque applied to trying to remove the screws was too much for the plastic molding on the panels to handle caused the clips and threaded inserts to strip preventing me from easily backing out the screws. Just something to be aware of on the panels and charge ports. This made 5 min worth of work turn into a hours of effort and a considerable amount of swearing. If you find the screws won't back out then I recommend using a solvent (like break cleaner) to help disolve the threadlock before going further to prevent a nightmare taking the mower apart. I wouldn't recommend using heat on the screw since it would likely melt the plastic. Not sure if anyone else had the same problem on their conversion or how they resolved this issue. I ended up needing to cut the old port out and pry out the threaded inserts that held it in place. If I had known how it fit together before I tried to take it apart I would have changed my approach. Lessons learned the hard way. I'll attach some pictures that show the original port, the replacement port, the modified replacement port, and what happens when trying to remove the port with the threadlocked screws if it strips.

Next up is doing the actual conversion, but likely going to wait a couple more months when the temps get cooler and grass mowing drops to about 1/month in case there are issues so that I'm not without my rider when I need it.

 

[eleven_brews]

Hello everyone - I did the 105Ah LiFePO conversion of my RM480e back in July and the results were fantastic. I went from being able to barely finish my 1/2 acre yard on a charge to getting 4 mows per charge.

However, I’ve recently run into a problem with the drive system. My mower now will usually not move unless I get a push to get going. Then if it does go, it has less power and throttle response and sounds like it’s struggling. The motor coils ohm out the same and the hall sensors all vary in voltage between 0 and 5v when turning the motor. The blades engage without an issue, so it doesn’t seem to be a battery issue.

Has anyone else run into this? It seems to point toward a bad drive motor controller, which is a spendy part. Does anyone have any troubleshooting steps specifically for the RM480e? I found a document for the zero-turn version.

 

[Ryobi_Rider]

Hello everyone - I did the 105Ah LiFePO conversion of my RM480e back in July and the results were fantastic. I went from being able to barely finish my 1/2 acre yard on a charge to getting 4 mows per charge.

However, I’ve recently run into a problem with the drive system. My mower now will usually not move unless I get a push to get going. Then if it does go, it has less power and throttle response and sounds like it’s struggling. The motor coils ohm out the same and the hall sensors all vary in voltage between 0 and 5v when turning the motor. The blades engage without an issue, so it doesn’t seem to be a battery issue.

Has anyone else run into this? It seems to point toward a bad drive motor controller, which is a spendy part. Does anyone have any troubleshooting steps specifically for the RM480e? I found a document for the zero-turn version.

I've read all the posts here and own one of the FB Groups. I have yet to hear of this symptom. I'm about to take on my own conversion project.

 

[Nizadar]

OK - so thanks to those on this thread I have my Ryobi 54" ZT mower up and running on 4 Chins 100Ah LiFePo batteries.
The biggest challenge was figuring out that I needed a precharge resistor to keep the battery's BMS from cutting out on the initial surge when the key was turned on. Solved that with a toggle switch and a 200 ohm power resistor.
Mowed the entire lawn today (about 2.5 acres) that was pretty overgrown and the batteries went from about 90% to 30%. That would not have worked with the original AGMs.

Plus side it is peppier due to lower weight.
Minus side it has lost some traction due to lower weight.
Big plus side I shouldn't ever have to replace these batteries in my lifetime, plus it was an interesting project, if a little nerve racking.


I can post more details if anyone is interested.

I have the same mower and CHINS batteries. Please provide more info as I'm going to be making the conversion soon.

"Solved that with a toggle switch and a 200 ohm power resistor" What & where did you buy and how/where do you install?

 

[icenov]

I'm sure it's not the LiFePO4 battery pack voltage. A fully charged lead-acid 48 V pack can sit at 56 V and even the DeltaQ charger that Ryobi supply with the 48ZTR will charge over 56 V when connected to the lead-acid pack. Even Ryobi wouldn't risk under-rating their caps by such an amount just to save a few cents. I've run my 48ZTR with a LiFePO4 battery pack for over 20 hours so far and had no issues. I suspect it was an unrelated failure.

An update - just blew a couple of caps (I think) in the deck motor controller! Mower wasn't under load, just driving (my wife was using it) and then bang and some sparks! Here's a photo of the controller board with holes where the 2 caps(?) were! Hard to tell what was there, as they are normally covered in resin. Note they aren't the big electrolytics...

 

[CharlesM99]

Hey all, can anyone tell me what kW motor your factory built electric mowers are running?
I'm considering doing a conversion on an old mower with a shot engine, and I'm hoping I could keep it at 10kW.
I'd use it mainly for towing around the property rather than actual mowing, so I'm not worried so much if it's under powered.

 

[icenov]

Some info in this post:

Hey all, can anyone tell me what kW motor your factory built electric mowers are running?
I'm considering doing a conversion on an old mower with a shot engine, and I'm hoping I could keep it at 10kW.
I'd use it mainly for towing around the property rather than actual mowing, so I'm not worried so much if it's under powered.

 

[jechin8]

I’m about to try out the “simple way” I have no time to build my own battery. My mower is brand new, it’s actually still at HD, I’m going to pick it up tomorrow. I’m going to order 4 of these battery's, the total with tax is about $1600. https://amperetime.com/products/ampere-time-12v-100ah-lithium-lifepo4-battery
They do free shipping and have a 3% off coupon. The battery has a built in BMS and they say they can run 4 in serial. Also the dimensions are the same as the OEM so it should be a drop in solution unless i’m missing something. The FAQs say it has a max 5120w load power. That would be the only thing i’m not sure of, what the mowers max load is, but I’m guessing it will be enough. I’m going to get a new charger and voltage meter as mentioned I should previously. Hopefully that is all I will need. I’m not sure how to wire up the charger snd meter yet, but I’m guessing it’ll be pretty straightforward. I’ll document the process and post here. I have to get the batteries shipped to a California address then shipped by boat to Hawaii so it may take about 3-4 weeks before I can do the swap.

Hi Zamondo,

I am interested in your success on the the drop in version. I've had my mower for 3 years and need to replace but I'm trying to find the simplest solution. Really trying to see if I can drop 4 of those amperetime batteries in and call it a day.

Did you need to change the charger?

 

[jechin8]

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.

I am really wanting to drop 4 12V 100AH in to replace. Can I use the existing charger? What charger did you end up using? How did you splice it?

 

[Sracer42]

I have the same mower and CHINS batteries. Please provide more info as I'm going to be making the conversion soon.

"Solved that with a toggle switch and a 200 ohm power resistor" What & where did you buy and how/where do you install?

Sorry for the delayed answer. I wired a series circuit from the battery side of the main contactor to a single pole switch - from other side to the switch to a 200 ohm 50W resistor and from the other side of the resistor back to the LOAD side of the contactor.
Flipping the switch allows the motor controllers etc to gradually charge up without the contactor engaging - thus avoiding inrush current when the contactor is engaged

Flip the precharge switch for about 5 seconds, then turn the ignition as normal - turn the precharge switch off. Mow away

 

[Nizadar]

Sorry for the delayed answer.

Thank you for the reply. I appreciate all the info I can get. It's the off-season now so I have a few months to prepare for spring. I'll be making the swap out over the next few months.

I wired a series circuit from the battery side of the main contactor to a single pole switch - from other side to the switch to a 200 ohm 50W resistor and from the other side of the resistor back to the LOAD side of the contactor.

I know very little about these types of things (all things being electric)... Can you explain this in more detail? Apologies as I'm learning Where did you get your 200 ohm 50W resistor (amazon)? I know what a single pole switch is thankfully

i.e.
battery side of the the main contactor ---> switch <--- [200 ohm 50W resistor] ---> load side of contactor

where is the battery side and where is the load side of contactor? (photos?)

I bought a 12V 15A charger and charged each battery up to 100% individually then connected all 4 of them in parallel. I'm not sure how long to leave them like this, but I read that this needs to be done to "balance" the bms's between the batteries.

I know how to wire them into series, but will then need a 48V charger. How do you charge yours? What make/model did you get?

 

[icenov]

Sorry for the delayed answer. I wired a series circuit from the battery side of the main contactor to a single pole switch - from other side to the switch to a 200 ohm 50W resistor and from the other side of the resistor back to the LOAD side of the contactor.
Flipping the switch allows the motor controllers etc to gradually charge up without the contactor engaging - thus avoiding inrush current when the contactor is engaged

Flip the precharge switch for about 5 seconds, then turn the ignition as normal - turn the precharge switch off. Mow away

I just replaced the slave deck motor controller and implemented your modification - but using a pack of 10 x 330 ohm resistors in parallel that I had from another project (so 33 ohms x 50 W). I checked with an oscilliscope and voltage stabilises after about 2 secs. Presumably that is OK? I suspect it can be left on as the contactor becomes a dead short when engaged - other than it will slowly discharge the battery if left on after mowing - is that correct?