Convert Ryobi RM300e to Lithium battery

[BillDeLong]

I just want to share my experience with a successful conversion I did to my Ryobi RM300e to Lithium.

My mower was about 18 months old when the stock lead-acid battery started losing capacity and would no longer mow our 1/3 acre lot on a single charge.

I found the following video extremely useful to do the conversion where the most important tip provided is at 20min into the video where he explains that you need to splice the yellow and red wires for the charger/relay bypass:

I discovered that there were 2 major concerns in that video that need to be addressed:

1) He states that it is necessary to replace the stock battery gauge where it's not compatible with lithium batteries and I have found that it works perfectly fine with the lithium battery I purchased

2) He uses a battery that is overkill and stupid expensive. I used the following article to come up with my own calculation for the proper size battery that I need:

Lithium Batteries Deep Cycle

www.blueheronbattery.com

Stock lead acid battery = 50Ah rated for 50% = 25Ah usable capacity

Ryobi states stock battery can mow 1 acre but my yard is only 1/3 acre so I figured I would have plenty of wiggle room with the following 20Ah battery that is designed for electric bikes:

Amazon.com

I simply used the included velcro straps to attach the battery to the rear chassis bar and charge/store the battery indoors to significantly extend the life of the battery which is stated as a 10 year battery lifespan!

The battery comes with a charger and 10AWG wiring which was fairly easy to splice solder to the included 8AWG harness that came with the mower. I have confirmed that the 10AWG wiring does not get hot, nor does the battery and the mower is far more powerful than it ever was on the lead acid battery. The battery gauge on the mower shows 2 bars left on the gauge after mowing my full 1/3 acre and the battery meter on the battery itself reads 25% charge remaining.

I couldn't be happier with the conversion and will be happy to post pics if anyone is interested in the doing the same conversion and wants to see my setup which isn't far from the video I posted above.


***UPDATE 25-AUG-2025
I have been running my conversion for close to 2 years with very good results and have been able to mow up to 2/3 acre with a 20Ah battery on a single charge.
I want to point out that the battery I purchased was recalled after several fires were reported by consumers, but I have chosen to continue using the battery because I believe the fires were caused by negligence of the users. Here's what I do to ensure proper/safe usage:
1) Store the battery between 50%-75% charge max inside a cool HVAC controlled environment
2) Only charge the battery immediately before use and monitor the battery during the charge
3) Visually inspect the battery case for signs of swelling and feel around the pack after each use for signs of any "hot spots" indicating a bad cell

More info here:

Understanding the Dangers of Lithium Batteries: Risks, Causes, and Safe Handling

IntroductionLithium-ion batteries have revolutionized how we power devices—fueling everything from smartphones and laptops to electric vehicles and industrial machinery. Yet, despite their high efficiency and energy density, these compact power sources carry inherent risks. Explosions, fires...

www.lithiplus.com

 

[donheller]

This is exactly what I was needing. Pictures of where you did the splicing would be fantastic if have one. Any pics will help.

Thanks for posting this!

 

[BillDeLong]

Glad to help, happy to report this eBike battery has been working great for the past 4+ months mowing once every 5 days on winter rye here in Central Texas, mower is significantly more powerful too!

For anyone who doesn't have soldering skills, you can send me the harness and I will splice solder the XT60 connector which comes with the eBike battery and bypass the relay with the yellow to red jumper connection for $25 labor + you include a return shipping label.

 

[bertsmobile1]

Unless you have bought the specific charger for that battery you are playing russian roulette with your house.
The vast majority of e-bike fires have happened because to owners were using a charger not designed for that specific battery.
Li batteries are not like Pb batteries where almost any charging cycle will do the job
There was a craze when Li batteries came out to fit them to custom motorcycles because they are tiny & can be hidden almost any where
This ended after dozens of then exploded , often taking whole workshops / man caves full of very expensive vehicles with them and even some houses .

 

[BillDeLong]

Unless you have bought the specific charger for that battery you are playing russian roulette with your house.
The vast majority of e-bike fires have happened because to owners were using a charger not designed for that specific battery.
Li batteries are not like Pb batteries where almost any charging cycle will do the job
There was a craze when Li batteries came out to fit them to custom motorcycles because they are tiny & can be hidden almost any where
This ended after dozens of then exploded , often taking whole workshops / man caves full of very expensive vehicles with them and even some houses .

Read the OP, charger was included with the battery, read the product specs on the Amazon link I provided if you have any further questions about the battery/charger combo I purchased.

I recommend storing the battery indoors to get the longest lifespan possible, (lithium batteries do not like heat) I also store the battery at 75% charge which will retain the maximum longevity of the battery, refer to the following article to understand why:

BU-808: How to Prolong Lithium-based Batteries

BU meta description needed...

batteryuniversity.com

 

[donheller]

When you say " bypass the relay with the yellow to red jumper connection" I see the connection that you would plug that splice into. But I for the life of me cannot figure out where you got the Yellow to Red connector to begin with?

 

[BillDeLong]

When you say " bypass the relay with the yellow to red jumper connection" I see the connection that you would plug that splice into. But I for the life of me cannot figure out where you got the Yellow to Red connector to begin with?

The wire that I spliced was the connector that fed into the relay switch, it's the only connector with a red/yellow/black wire going into it, leave the black wire cut, and splice the yellow/red wires together, throw away the relay switch which feeds into the old charge plug, I also tossed out the charge adapter too. The relay is a safety feature that prevents the blades from being turned on if you have the charger hooked up, but this is no longer needed when you convert to lithium because you will not be using the original charging system anymore.

 

[BillDeLong]

Just an update, it's been 6 months since I have been using the eBike battery and I couldn't be happier with the results. I do think it's worth pointing out that even though the gauge on the battery will read a full charge, it may take an hour or longer for the charger to shut off the fan and that's when you know the battery has truly reached a "full saturation charge". I have found that mowing my 1/3 acre yard will leave the battery at 3/4 charge after a full saturation charge but may leave as little as 1/4 charge if I stop the charger immediately when the monitor reads full which is a false full reading.

No doubt the battery I am using can easily mow a full acre on a full saturation charge.

I am careful to store the battery indoors and leave it at 50% charge to get the longest possible lifespan out of the battery, I only charge it the night before I plan to mow:

BU-808: How to Prolong Lithium-based Batteries

BU meta description needed...

batteryuniversity.com

 

[BillDeLong]

*** RECALL WARNING ***

The battery I linked above is no longer available and the vendor has removed themselves from the Amazon store that I purchased it from. I just received an email from Amazon telling me that the battery I bought was recalled for safety issues where there are have been 13 reported fires to date, more info here:

CPSC Warns Consumers to Stop Using Unit Pack Power (UPP) E-bike Batteries Due to Fire and Burn Hazards; Risk of Serious Injury and Death

www.cpsc.gov

Basically I'm SOL with no way to get any recourse from Amazon because my purchase is outside of their 30-day protection period and the seller has shut down with no option to send me a replacement.

There is no information provided about the root causes for the fires which forced the recall, but I am going to choose to continue using the battery based on my previous experience with observing LiPo fires due to abuse around racing radio controlled cars. Essentially, heat is the #1 cause to premature battery failure, so storing a lithium battery in a hot garage is a very bad idea as heat tends to increase voltage so keeping a battery on a full charge will compound the risk with heat which tends to cause the cells to swell up. Once there is any visible signs of the plastic case swelling then it's time to discard the battery. Almost every LiPo fire I've seen at the race track was confirmed by the owner who knew they had a very old battery that was swollen and needed to be replaced but they kept using it anyway. Another prime time when fires occur tend to be when the battery is being charged. Not all batteries have the ability to balance their cells and the cell closest to the true negative tends to get worked the hardest and not having the ability to measure the internal resistance of these cells increase the risk over time. More info here:

LVC Adjustments and Packs in Series

www.smc-racing.net

That said, it's extremely important to be near the battery when it's being charged, if you start to hear any popping/crackling sounds, then you typically have about 10 seconds before billowing smoke erupts from the battery, and then you have maybe 5-20 seconds after that before actual flames erupt. You need to act extremely fast and get the battery outdoors during those precious seconds before smoke and/or flames erupt. I have had to kick a battery pack with my foot in full flames to get it outside our pit room at the race track when other drivers left their aged batteries unattended during a charge cycle. I have learned to replace my RC Car batteries after 1 year of use because they tend to be heavily abused, however it's not uncommon to see packs last between 3-5 years before usable capacitance fades on batteries that I haven't abused.

I will keep a close eye on this battery and provide a follow-up when I feel it's time to discard the pack, I can guarantee it won't last the 10 years that was falsely advertised by the seller!

 

[Tiger Small Engine]

*** RECALL WARNING ***

The battery I linked above is no longer available and the vendor has removed themselves from the Amazon store that I purchased it from. I just received an email from Amazon telling me that the battery I bought was recalled for safety issues where there are have been 13 reported fires to date, more info here:

CPSC Warns Consumers to Stop Using Unit Pack Power (UPP) E-bike Batteries Due to Fire and Burn Hazards; Risk of Serious Injury and Death

www.cpsc.gov

Basically I'm SOL with no way to get any recourse from Amazon because my purchase is outside of their 30-day protection period and the seller has shut down with no option to send me a replacement.

There is no information provided about the root causes for the fires which forced the recall, but I am going to choose to continue using the battery based on my previous experience with observing LiPo fires due to abuse around racing radio controlled cars. Essentially, heat is the #1 cause to premature battery failure, so storing a lithium battery in a hot garage is a very bad idea as heat tends to increase voltage so keeping a battery on a full charge will compound the risk with heat which tends to cause the cells to swell up. Once there is any visible signs of the plastic case swelling then it's time to discard the battery. Almost every LiPo fire I've seen at the race track was confirmed by the owner who knew they had a very old battery that was swollen and needed to be replaced but they kept using it anyway. Another prime time when fires occur tend to be when the battery is being charged. Not all batteries have the ability to balance their cells and the cell closest to the true negative tends to get worked the hardest and not having the ability to measure the internal resistance of these cells increase the risk over time. More info here:

LVC Adjustments and Packs in Series

www.smc-racing.net

That said, it's extremely important to be near the battery when it's being charged, if you start to hear any popping/crackling sounds, then you typically have about 10 seconds before billowing smoke erupts from the battery, and then you have maybe 5-20 seconds after that before actual flames erupt. You need to act extremely fast and get the battery outdoors during those precious seconds before smoke and/or flames erupt. I have had to kick a battery pack with my foot in full flames to get it outside our pit room at the race track when other drivers left their aged batteries unattended during a charge cycle. I have learned to replace my RC Car batteries after 1 year of use because they tend to be heavily abused, however it's not uncommon to see packs last between 3-5 years before usable capacitance fades on batteries that I haven't abused.

I will keep a close eye on this battery and provide a follow-up when I feel it's time to discard the pack, I can guarantee it won't last the 10 years that was falsely advertised by the seller!

A potential firebomb in your garage. I would store it outside under cover away from your house.