An e-bike battery-bank design conundrum (on a quad, no less) ... nice!
The e-bike vendor got away with 5 x 12v70ah FLA batteries as there was no bms involved ... just a single series string of 5 12v FLA batteries ... easy to monitor, easy to charge.
We can't "easily" flip to 5x 12v LiFePO4 batteries, because most vendors probably have a limit of 4 bms's (4 x 12v batteries) in a single series string; usually, this is because they didn't test anything beyond that, and therefore won't support it, or their bms is home-grown, and can't support it. On this site, we normally deal with 12v/24v/48v battery-bank designs, to match our inverter designs. There's explicit/implicit rules for battery-banks ...
In theory only ... only thing I could think of for your 60v LiFePO4 battery-bank is to string 5 LiFePO4 batteries together in series for output of 60v, but "break them apart" for separate charging at 12v each, thus side-stepping the rule of "no more than 4" (while charging); each bms acts together for output, but on its own for charging/input. No vendor would probably support this, but you could ask them via their support mechanisms. If they don't see a problem with 5 bms's acting together on output, maybe they would allow it.
This could be dangerous on the charging (input) side, involving bus-bars, cabling, and "break the battery-bank apart" switch designs, but with lots of head-scratching, you can decide if you are comfortable with the effort and operation, to get to LiFePO4; things could fry if you aren't careful/diligent on the charging side (setting up charging each cycle).
It has a slight advantage of keeping things simple (off the shelf LiFePO4 batteries), at the cost of cabling & charging complexity. In other words, you don't have to build a pack from scratch. You'll still have to "engineer" the monitoring and charging, as FLA is out, and LiFePO4 is the technology in use. Can't reuse the old FLA engineering that came with your quad ...
Hope this helps ...
