Rescuing a Ryobi Electric Riding Mower: Lead-Acid to LiFePO₄
A neighbor was about to discard a Ryobi RM480EX riding mower, assuming it was only a dead battery issue. He demonstrated the blades still worked, but the drive wheels wouldn’t engage. I took the mower home and removed the stock lead-acid batteries. After testing, I found one cell well below voltage and opted to replace the entire pack with a 48 V lithium iron phosphate (LiFePO₄) battery.
YouTube Video: https://youtu.be/HhnOW3vln00
The mower itself was in excellent condition, nearly new really. I stripped off all the panels and gave it a deep clean. After installing a temporary 48 V battery, the mower still wouldn’t move, it would just twitch slightly when pressing the pedal. I began a full diagnostic process.
I hadn’t worked on an electric riding mower before, though I do own a Ryobi 40 V walk-behind model. The symptoms pointed toward a control input issue, possibly the pedal’s potentiometer. I tested it: voltage output was normal (0–5 V depending on depression). That ruled it out. I suspected either the motor controller or the motor itself. I then realized my temporary battery (a general-purpose off-grid unit) wasn't ideal for motor loads. It had a 15s configuration (max ~54 V, nominal ~48 V), not the 16s layout designed for traction systems.
I upgraded to a LiTime 48 V 100Ah LiFePO₄ battery rated specifically for golf carts. This battery can handle sustained discharge, has surge current capacity >200 A (2C 120 sec), and a profile more suitable for drive motors. The large 100Ah capacity also is basically double the 80 volt proprietary versions.
Once I replaced the motor controller (996508001 - DRIVE MOTOR CONTROLLER) that solved the drive problem and it was like brand-new, really better because of the battery was so improved over the original.
Performance Results After a full charge, I mowed roughly 1.5 acres (75 minutes) and still had 79% battery remaining. This setup could easily mow several acres or travel up to 40 miles per charge. Using the LiTime monitor mounted to the steering column, I logged detailed power usage: Without blades: draw averaged 500–800 W, with spikes to 1.5–2 kW under max pedal or uphill. With blades on but stationary: 1.5 kW spike, settling to ~1 kW. Blades engaged and driving: total draw hovered between 1–1.5 kW, maxing at 3 kW on hills with both systems running. Interestingly, the mower regenerates power during braking or downhill driving, further extending range.
Why This Model Works Well for Conversion The RM480EX originally used heavy lead-acid batteries and has a robust steel frame. Unlike modern mowers with proprietary battery packs or over-the-air connections/updates, this one allows any 48 volt battery setup so you can retrofit it easily. That makes it especially attractive for users who value long-term serviceability and dislike app-tied tool ecosystems.
Battery Chemistry Matters: NMC vs. LiFePO₄ Many new commercial 80 V riding mowers (Ryobi, Ego, etc.) use nickel-manganese-cobalt (NMC) lithium-ion packs. While energy-dense, NMC cells are sensitive to deep discharge and cold temperatures. Common problems include: BMS lockouts after deep drain or winter storage. Melted connectors/arced contacts from high current surges. Early pack death after only 2–3 seasons of use due to thermal or voltage stress. In contrast, LiFePO₄ batteries tolerate deep discharges, store well during off-season, and are thermally stable. A properly rated BMS (100 A+) ensures safe, reliable performance. While heavier and less energy-dense, they offer greater cycle life, better cold-weather performance, and reduced risk of thermal runaway.
Here's the stats for the LiTime:
EV-graded LiFePO4 Cells:
- 4,000 cycles at 100% DOD
- 6,000 cycles at 80% DOD
- 15,000 cycles at 60% DOD
That means you can charge and discharge everyday to 100% for 4000 days! That is more than 10 years! The likelihood you could even use it like that is doubtful. In essence I will never need another battery for the life of my use.
| Feature | 80 V NMC (Ryobi, Ego) | 48 V LiFePO₄ (Retrofit) |
|---|---|---|
| Nominal Voltage | 72–80 V | 48 V |
| Energy Density | High (180–250 Wh/kg) | Moderate (90–140 Wh/kg) |
| Deep Discharge Tolerance | Poor – BMS lockout risk | Excellent – recoverable |
| Winter Storage | Must maintain SOC | Stores well long-term |
| Cycle Life | 1,000–1,500 cycles | 4,000+ cycles |
| Connector Reliability | Arcing/melting common | Low risk (with good BMS) |
| Cold Weather Discharge | Poor | Reliable to –20 °C |
| Thermal Stability / Safety | Moderate (risk of fire) | Very high (inherently safe) |
Charging the Battery
The original charger that comes with the RM480EX is designed for a 48 volt lead-acid battery. This means you can't use it to charge any other chemistry. When you have a 5KWh battery like a 48volt 100Ah design it's nice to be able to charge it as fast as possible. I choose to use the LiTime 30A charger designed for LiFePO4 Batteries. Because of the high 30A charge rate I was unable to use the built-in rear port. The wiring is not designed for 30A and would be dangerous to use. I was easily able to bypass this and directly connect to the battery with the included anderson connectors and wiring provided right under the seat.
With this charger I can add about 1.5Kw and hour. That means a dead battery would take about 3 ½ hours to charge. Another way to look at it is that in a mere 45 minutes you can get enough charge to do almost an acre and a half. Even at $0.20 a kw hour you can cut your 1 acre lawn for 20 cents.
This retrofit turns the RM480EX into a highly efficient, low-maintenance electric mower with longer runtime, better battery longevity, and reduced seasonal issues. For anyone inheriting or salvaging one of these older Ryobi models, a properly matched LiFePO₄ battery may be the best upgrade possible. And you save a couple hundred pounds going from lead-acid to LiFePO4.
Parts I installed:
Battery: https://www.litime.com/products/48-volt-100ah-golf-cart-lithium-battery?variant=46077269213404
Monitor: https://www.litime.com/products/rs485-battery-monitoring-display?variant=45804662128860