I've been following this forum for a few years now. I have a Ryobi RM480E mower (purchased in 2018) and my original batteries lasted 5 seasons. I experienced many of the same issues that others have described. Early this year, I replaced the original batteries with the Mighty Max SLA 100ah batteries. I had already purchased the new SLA batteries before I discovered YouTube videos showing how to upgrade the batteries to Lithium LiFePO4. Since I had already committed to another set of SLA batteries, I thought maybe I could position myself better for a future Lithium upgrade and possibly get some benefit at the same time with my new SLA batteries.
So I purchased the suggested charger that can charge both SLA and Lithium batteries and I installed the suggested gauge that can also handle both battery types. In doing so, I now know that my charger is recharging my SLA batteries after each mow because it has a display that shows me exactly what is happening, unlike the OEM Ryobi charger which I think many times was not really doing a recharge even though it was flashing green. I also now have a gauge that shows me my current Amp Hours / Voltage / Capacity Percent that seems to be pretty accurate. I probably spent less than $225 and the YouTube videos show what adaptations are necessary to make things work...they are not really difficult. I chose to reuse the OEM charging plug to replace what came with the new charger so I can easily plug into the RM480E charging port...again pretty simple to accomplish. The YouTube videos do a good job of explaining what needs to be done.
I don't have a long term use report, but after one cutting season, my new MM SLA 100Ah batteries still show 100% capacity. I will see how the batteries look after they over-winter in a NC garage where temps are fairly moderate.
With Lithium batteries probably declining in price in the future and the possibility of me getting more than 5 seasons out of my current MM SLA batteries due to a "better" charger, I felt the extra expense at this point made sense instead of just continuing with the same setup. The lithium batteries shown in the videos have a similar form factor to the MM SLAs, ie, they fit in the Ryobi battery tray nicely.
Here is the YouTube video I found most helpful...
https://www.youtube.com/watch?v=8qRRcIc0mgQ
