I bought an electric, zero-turn riding lawn mower three years ago. I knew when I bought it that the battery life for its lead-acid batteries would be short. Like in a golf cart, you can expect 3 to 5 years out of a set of AGM lead-acid batteries like those that came in my mower. After that, their ability to hold a charge begins to fade. Lots of the online reviews of electric mowers confirmed this would be true for the mower I bought, a Ryobi ZT480e.
Now-a-days these mowers come with lithium-iron-phosphate (LiFePo) batteries. These types of batteries are dramatically better than AGM lead-acid in several ways:
- Longer run time: AGM lead-acid battery manufacturers tell you that repeatedly running the battery down past 50% of its capacity shortens the battery’s life. That’s not true for LiFePo batteries. They can be repeatedly run down to 0% without reducing their life span. This means that, on a single charge, a LiFePo battery can be used to mow for twice as long as a lead-acid battery with the same capacity rating.
- Longer lifetime: AGM lead-acid batteries are expected to last in service 3-5 years before they lose their ability to hold a charge. LiFePo batteries are expected to last 5-10 years.
- No power loss over time: As a lead acid-battery is discharged, the voltage it supplies drops. This means that, as you mow, the mower becomes weaker and weaker. This does not happen with LiFePo batteries. Their voltage only drops a few tenths of a volt as the battery’s charge is consumed. At the very end, when the remaining charge drops below 10%, voltage then drops more steeply. I didn’t realize how big a difference this made until after I installed the LiFePo battery in my mower. I get a much cleaner cut now. My mower has the power to slice the grass blades more evenly and does not bog down nearly as often as it used to. My lawn looks noticeably better after a mow now than it did before.
- Smaller and lighter weight: My mower came with four 12-volt, AGM lead-acid batteries that weighed a total of 200 pounds. I replaced them with a single 48-volt LiFePo battery that weighs 83 pounds. The battery I chose has 30% more rated capacity than the AGMs (100Ah vs 75Ah) and a 20% smaller footprint. When taking into account the 50% limit on discharging AGM batteries, the LiFePo effectively has more than twice the capacity.
The battery I used was the DC HOUSE 48V 100Ah LiFePO4 Golf Cart Battery & Charger with Bluetooth. DC House is a Chinese company and I rate it as something of a risk as I’m not sure how strong the support behind it actually is. The listing does say that it has a 3-year warranty and the fact that I bought it with my American Express card extends the warranty for an additional year, so that’s something. We’ll see.
Like all lithium batteries, this one has a battery monitoring system (BMS) built into it. This is a small computer that manages and balances the charge in each of the individual cells that go together to make up the battery. This particular BMS also provides a Bluetooth connection that allows a mobile phone app to view battery statistics. This means that there’s no need to buy or hook up a separate battery monitoring device as is usually done with most lithium battery setups. This battery does come with a monitor that could be mounted on the mower, but all that does is connect to the battery over Bluetooth and show the same statistics as the mobile app. I haven’t tried it, but according to what I read, the monitor and the mobile app cannot be used at the same time, only one device at a time can connect to the battery via Bluetooth. I have elected to use the mobile app and I haven’t bothered to install the monitor panel.
There is one statistic this monitoring setup does not provide. There’s no hour meter that tracks total mower usage. The original battery meter on the mower does have this and that’s made me leave that meter in place, even though the remaining charge percentage it displays is meaningless. (The meter calculates remaining charge based on the battery’s output voltage. Since LiFePo batteries don’t experience the same voltage drop as they are discharged that AGM batteries do, the meter thinks the battery is at 100% all the time, until suddenly, at the end, it isn’t.) If I need to know the remaining charge while mowing, I stop and check the mobile app on my phone.
The physical installation of the battery is straightforward and there are tons of videos on YouTube demonstrating the process. I’d emphasize a couple of things based on my experience:
While the AGM lead-acid batteries are heavy, there’s no need to spend money on equipment like lift-tables or wooden platforms to remove them. All that’s necessary is to have something to support one end of the battery tray as you pull it out. I used the floor jack I use for my cars for this purpose, but a regular scissors jack from your car’s trunk, or anything similar would work just as well.
To make things easier, don’t wait to remove the batteries until you have the battery tray pulled out all the way. Take the first two batteries out with the tray extended half-way, then deal with the remaining two batteries.
To do this, work through the battery door on the top of the mower to first loosen the battery hold-down bracket. Unscrew the main battery connector from the bracket as well as the small device on the opposite side of the bracket. (That’s called the “charger lockout circuit”.) Then slide the plastic covers out of the way to expose the short jumper cables that connect between the front and back rows of batteries and take those jumpers off. To prevent accidental damage, disconnect all of the small wire connections that go in and out of the battery charging receptacle. Slide the battery tray out part way to expose the front terminals of the front row of batteries and remove the cables from those terminals. Slide the tray out some more and lift off the front row of batteries.
Slide the tray out most of the rest of the way, leaving the back edge of the tray still in it’s track and resting the front edge with the pull handle on the floor jack (or whatever it is you’re using.) Remove the jumper that connects the two rear batteries and remove those batteries from the tray.
Once the batteries are removed, the battery tray itself should be lifted out and cleaned. I also cleaned out the interior of the battery compartment. There was lots of debris in there after three years of mowing.
I removed the battery spacing bars at the front and rear of the battery tray. Knocking out the spacers in the center of the tray was easy, they’re only held in with double-sided tape. Some of that tape stayed stuck to the battery tray and that turned out to be a good thing. It served to help keep my new battery in place and prevent it from sliding around.
I put my battery in the center of the tray, pushed up against the rear of the tray. I cut wooden blocks to center the battery side to side and to prevent it from sliding around. I looped a ratchet strap over the battery and the battery tray to hold the battery down. I only tightened this until it was snug. I didn’t want to put too much pressure on the battery case.
I drilled holes in the bottom front frame of the battery tray to mount the battery charger inside the mower. Be sure to put the bolts holding the charger in from the bottom so that they don’t stick down too far and interfere with the mower frame when you slide in the battery tray.
I used a hole saw to make a hole to the left of the existing charging port and mounted a shore power adapter there. Make sure it is over to the left far enough that its cord doesn’t conflict with the battery when the battery tray is slid in. After the tray was slid in I plugged the charger into this adapter. When I want to charge the battery, all I have to do is pop open the shore power cover and plug an extension cord into it. If I want to check that the charger is working, I can use the mobile app to do that, no need to see the indicator light on the charger itself.
I initially tried to remove the old battery charging port from the mower when I connected my new battery. This didn’t work out. The mower would not turn on with the key until I reconnected everything on the changing port back the way it was originally. I haven’t taken the time to figure out what the critical parts of that circuit are. I did look to see if someone else had figured this out, without any success. I ultimately decided I don’t have any pressing need to solve this problem and that things are fine the way they are. I did 3D print a plug that I stuck down into the old charging port to prevent any accidental connections being made in there.
Warning: The “charger lockout circuit” I mentioned earlier prevents the mower from being driven away while the charger is plugged in. I mounted my new battery charger inside the mower and connected it directly to the battery terminals. Doing this bypasses that lockout circuit and means that the mower can be driven away while it is plugged in and charging. If preserving this protective feature is important to you, there are ways to install the charger so that it uses the existing changing port circuitry and protections. These are described in the various how-to YouTube videos. There you go, you have been warned.
So that’s about everything I learned doing this project. If you’ve read this far, then I hope this was helpful. I’ve only mowed twice since doing this project. So far, so good.
