Background

Lead Acid

Ryobi 48V mowers came with four 12V lead acid batteries wired in series to create a 48V battery bank. The voltages here are considered nominal voltage and are not the actual voltage. The actual voltage of each battery is closer to 13.15V when it's fully charged and 52.6V for the battery bank, but it will vary depending on the batteries, their condition, and temperature. Lead acid chemistry produces 2V per cell. Again these are nominal values and the actual voltage is a little higher. Each 12V battery has six 2V cells. To produce 48V, we need 24 cells or 4 12V batteries.

LiFePO4

LiFePO4 (read this as lithium iron or lithium iron phosphate) cells are 3.2V nominal. To get a similar voltage to a 48V lead acid battery, 16 cells are wired in series for 51.2V nominal. You will sometimes see this listed as 16S LiFePO4. While the fully charged voltage ends up being a little higher than lead acid, it's still within the acceptable range and this provides two benefits. The first is that the charging voltage is almost the same as the lead acid. The second is, through most of the discharge, all the way down to 20%, the LiFePO4 will provide voltage equivalent to a fully-charged lead acid battery.

While this is all interesting, the main thing you need to know is you may see LiFePO4 batteries listed as 48V or 51.2V, sometimes both for the same battery. The 48V refers to the lead-acid equivalent nominal voltage and the 51.2V refers to the LiFePO4 nominal voltage. Just make sure the battery has 16 cells or a rated voltage of 51.2V.

What about 4 x 12V LiFePO4?

You may have seen 12V LiFePO4 batteries. These each have 4 cells in series, so putting 4 in series will get you the 16 cells you need. Since the stock batteries are 4 x 12V, you might think this is a good option. Let's look at the pros and cons.
Pros:

• If you get batteries close to the size of the stock batteries, you can mount them in the exact same way.

Cons:

• The batteries can become imbalanced, causing charging or operating issues

• Batteries often aren't rated for as high of a current load

• More connections

• More components leading to higher chance of failure

• More difficult to remove the battery (If it gets colder than -4°F / -20°C where you store the mower, you'll want to store the battery inside) 

As you can see, the cons outweigh the pros, so I will only be listing 48V batteries here.

50Ah Batteries

When this battery came out  at the end of Summer 2024, it lowered the price point for 100Ah batteries and has shown to be just as reliable as it's 50Ah little brother. It commonly sells for $660 on eBay with a coupon and occasionally $640 (no sales tax) with a coupon on DCHouse. 

You can buy this battery directly from DCHouse, from eBay, or from Amazon. In all cases, it will ship from the same place. Most North American shipments come from a warehouse in California. There are regular sales on eBay, usually requiring a coupon code. Less often, but usually a better deal, there are sales on DChouse's website. Amazon sometimes has coupons too.

Links:

• DCHouse (No sales tax)

  • Use coupon code 5FROMYOURFRIEND for 5% off

• eBay Listing 1, eBay Listing 2, eBay Listing 3

  • DCHouse has multiple eBay listings. One may be cheaper, but be sure to see if there is a coupon listed.

• Amazon

You can also get this battery with an 18A charger. It's usually  $100 more than buying that battery alone. While this is a good charger,  it doesn't come with a charge plug and is more intended as an on-board charger for use in golf carts. I wouldn't use it on-board on a mower because it can become caked in debris and overheat. To use it externally, you can add an EZGO RXV charge plug, but it's easier to buy a different charger that  already comes with one.

With 18A charger:

• DCHouse (No sales tax)

  • Use coupon code 5FROMYOURFRIEND for 5% off

• eBay

• Amazon

RM300e Options

The RM300e differs from the other RM480 and ZT480 in that the battery tray does not slide out the back and the mower is smaller overall. Some space can be gained by cutting the angle iron the surrounded the bottom of the stock batteries. Many have reported this allowed use of the DCHouse and Chins 100Ah batteries listed above, but the fit was still tight. Below are listed smaller options that other have reported success with.

Self-Heating Options

If you live in a very cold climate, use your mower as a snow plow, and store it in an unheated space, you may want to consider a self-heating battery.

Normally a LiFePO4 battery needs to be above 32 F / 0 C to charge. A self-heating battery has a resistive heating pad built into the battery. When the charger is connected below 32 F / 0 F, the battery will use power from the charger to heat the battery to a safe charging temperature before it begins charging.

This does not effect the operating temperature of the battery, which is -4 F / -20 C, however if you charge your battery before operating it, this will preheat the battery to a safe operating temperature.

With most Bluetooth-enabled models, you can monitor the internal temperature of the battery.

135Ah - 150Ah Batteries

Do you need batteries this big? If you need to mow more than 3 acres or are using your mower as a power bank, then maybe. The sweet spot for dollar per Amp-hour is in the 100Ah batteries, so you do pay a premium for going bigger. But if this is what you need, here are some options. None of these will fit in an RM300.