Ryobi's 48V mowers came with four 12V lead acid batteries connected in series. These batteries were likely picked to fit a specific price point and because many components in these mowers were inspired by golf cart designs in which this battery configuration is common. There are several problems with this configuration.

The first is that the batteries become unbalanced over time resulting in uneven degradation.

The second issue is lead acid batteries are not well suited for the power needs of a mower. These mowers can pull a lot of current for a sustained amount of time, especially when the grass is tall and/or wet. While they will do the job, repeated use like this shortens the battery life.

The third problem is lead acid batteries can be permanently damaged when the capacity falls below 50%. Many people who bought these mowers didn't realize this and the gauge the mowers come with would seem to indicate this as more of a caution, displaying 30 - 50% in yellow rather than red like 0 - 20% is displayed.

The final issue has to do with the voltage curve of lead acid batteries. As you can see from the chart. The voltage with this chemistry falls rather steeply. As the voltage falls, more current is pulled from the battery to maintain the same power. This is normal for most battery chemistries, but is more pronounced with lead acid. The problem is some components don't handle the lower voltage or high current very well and it can cause glitches. Many owners of Ryobi 48V mowers running stock batteries report strange behavior like jittery movement and sudden loss of power. These are indicators of low voltage and that either the batteries have failed, are failing, or have been run down to below their usable state of charge.

All these factors result in a common complaint, that the runtime of these mowers falls quickly. While there is the rare individual claiming 5 years running on the original batteries, much more common is someone with failed batteries on a 1 - 3 year old mower.

The Solution: LiFePO4

Ryobi had a 1 year warranty on these batteries and some people were able to get them replaced for free. Though some of those people had to wait a very long time for the replacements. Even then, many reported having the same issues in less than a year.

What many have done is replace the stock batteries with LiFePO4. You may also hear them refered to as lithium iron, lithium iron phosphate, lithium ferrophosphate, or LFP. While this is a type of lithium ion battery, it is a different chemistry from the lithium ion batteries in your phone and laptop. It is heavier, cheaper, and very stable. Cheap and stable make it a great choice for these mowers. And while it is heavier than other types of lithium batteries, it is 70% lighter than lead acid.

LiFePO4 has one more advantage. As you can see in the chart, LiFePO4 batteries have a much flatter voltage curve, so you have very consistent voltage regardless of the state of charge. LiFePO4 batteries also have a larger usable capacity. This means either you can get longer run time from the same capacity (measured in Amp-hours) or you can use a smaller battery and maintain the same run time.

When to replace your batteries

The classic symptom of failed batteries is your mower will only drive a little bit, then it stops and you get 5 beeps. This indicates the voltage is below 48V under load. Sometimes turning it off and then back on you can drive a little more before it happens again.

But you may want to consider doing a battery conversion before your batteries fail. There are three benefits to this.

The first is you'll get more money for your old batteries, which can offset the cost of the upgrade. More on this below.

The second is you can do it when you don't need your mower, November, for example. That way, if you have any issues, you have time to sort them out without worrying about the grass getting too long.

The third is operating on failing batteries causes components to operate under the voltage they are designed for. This means they pull more Amps in order to do the same work. Increased amperage means increased heat and heat kills electronics. Running your mower until it won't go anymore increases the chances of a secondary failure like a motor controller.

Shopping list

For a more speciic list of recommendations, see the Lithium Upgrade Cheatsheet.

Battery

You can learn about battery options here.

Battery Hold Downs

You need some way of securing the battery to the mower. In the RM300e this means directly to the frame. In the other mowers the battery can be secured to the battery tray, making it easier to remove if you need to.

The simplest and most common solution is to fill the space around the battery with wood scraps and put a tie down strap around it.

I like to make metal brackets for mine using angle iron. This is definitely overkill, but it looks really nice.

Whatever option you go with, the important thing is the battery can not move independent of the frame.

Charger (Optional)

Your stock charger will charge LiFePO4 batteries, but, depending on which stock charger you have, you may still want to consider an aftermarket charger. More information on this and a look at some charging options can be found here.

Battery Meter (Optional)

The stock battery meter won't be accurate. While a meter is nice to have, if your battery is over-sized for your yard you can get away without a meter. Some batteries also come with Bluetooth, allowing you to monitor the battery with your phone. That said, it's definitely easier to glance down at a meter than to keep the app open on your phone.

You can find more information on battery meter options here.

What about ... ?

Soft Start

You might hear some people talking about installing a soft start bypass or kit on their mowers when they do a conversion. What this does is temporarily limit the current that can be pulled from the battery, usually just for a few seconds when you first turn on the mower. This allows the capacitors on the controllers to charge more slowly. Previous generations of LiFePo4 batteries had lower peak current, so a soft start was often needed to prevent the battery's BMS from shutting down when too much current was pulled when the mower was turned on. Batteries have gotten better and this is usually no longer necessary. My advice is to skip the soft start and make sure you get a battery that can handle a peak current of at least 150A. If you run into issues with the BMS tripping, you can always add a soft start kit later.

What's involved in the conversion?

I'll try to make a more detailed page or a video about this. But here are the main steps.

Remove your old batteries
Secure the new battery to the battery tray or frame. (See the battery hold downs section above)
Connect the main battery cable to the new battery's terminals. Red to positive, black to negative. If you're using a battery meter with a shunt, you'll want to add the shunt between the black cable and the negative terminal. As long as you have space it is fine to attach the shunt directly to the battery terminal. If the bolts that came with the battery aren't long enough for this, you can use one of the bolts that came with the meter. Just add a flat washer and locking washer on top of the shunt before inserting the bolt.
If your mower has a battery tray, slide it back into the mower and install the two bolts that hold it to the frame. Be sure to place the fat washers between the tray and the frame. There is usually still a small gap left. Use one or two 5/16 washers to fill this space before tightening the bolts. If you don't, the front end of the tray will lift up when you tighten the bolts and the whole tray will bounce when you drive.
If you are installing a meter, go ahead and install it now. Or you can wait and do it once you've tested everything. More information on this in the Battery Meter Options page.
Connect the Anderson connector. This is the big grey plastic connector the battery cables go into. Make sure the connector is secured to something. You don't want it bouncing around and coming loose. Whenever you work on your mower's wiring, you'll want to disconnect this first to avoid any accidental shorts.
If you're using an aftermarket charger, break the tabs off the inside of the mower's charge port using a small pair of pliers.
Fully charge the battery.
Test it out!

As you can see, it's not that complicated. The hardest part is making sure the battery is secure and that's really not that hard. If you run into any issues, you can get help in the Ryobi 48v Riding Mowers Facebook Group.

What do you do with your old batteries?

If your batteries are still good, you can sell them on Facebook Marketplace. I listed my 100Ah 12V lead acid batteries for $70/each and they were gone within a few hours. They are very popular for use with solar and electric fences.

If your batteries have failed, you can get $8 to $10 for each them at a scrap dealer. Some auto part stores like Advanced Auto and AutoZone will you a $10 gift card for each battery you bring in.

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