I have an older electric lawn mower (model RM480e 38" 75 AH) that originally had 75AH lead acid batteries and they have reached the end of their life. I recycled the old lead acid batteries then acquired 16ea 90AH LiFePo4 (LFP) batteries and a BMS. Here is a quick overview and thoughts about the upgrade. Even though in my video I used a 15 series cell pack I suggest sticking with the standard 16 series cell pack.

The result:
The mower was advertised to mow 2 acres and mine did do that. Of course if the grass was getting long it wouldn't quite mow the whole yard, I would finish it the next day after it charged over night. After the LFP upgrade I have no problems mowing my 2 acre yard twice and if the grass gets long.

Lets compare cost ...
___ If replaced with lead acid batteries:
* 75Ah lead acid battery 4pcs at $150 each
= $600 total
=== VS ===
___ Upgrade to LiFePo4 (LFP) batteries:
* 90Ah LFP X 16pcs $648
https://s.click.aliexpress.com/e/_Ddm...
* 7S - 24S ANT Smart Bluetooth BMS 60A / 150A peak $46
https://s.click.aliexpress.com/e/_DBw...
= $ 694 total

With this upgrade you can use a phone to check the battery status OR you can install install the LCD option gauge for $16 more.

___ Chargers:
I suggest selling the original 48V charger on eBay. They are also used for golf carts so they are in demand. List it for both the Ryobi mower and the golf cart "Delta-Q SC-48 EZ GO". They sell for about $200- $400!! With that money you can buy a 58.4V 16 cell LFP charger like this 10A waterproof one for $135 https://s.click.aliexpress.com/e/_Dl5... or this indoor 10A one for $25 https://s.click.aliexpress.com/e/_DlL...

I am thinking over the next few years as these mower age this might be a popular upgrade. As you can see the cost difference is negligible if not considerably less if you consider selling the old lead acid charger; meanwhile LFP batteries are only getting cheaper. In addition LFP batteries have a 3000-4000 cycles an they don't have a battery memory issue nor do they need to be stored on a trickle charger. To store charge the LFP batteries to about 75-95% before storage then check them every 2 months. I only mow about 10 times a year so there is no doubt the batteries will rot away before the they reach their cycle life unlike the original lead acid batteries that are rated for only 250-300 cycles ... what a big improvement!

Cheers!
Hold on while I overthink this.