Here is a fossil fuel powered mower that has been converted to run on electricity instead.
"Upstate Electric" blog
Enerdel lithium batteries configured in a 100-lb swappable pack
ME-1004 motor has the same shaft size as original engine
Soliton Jr. controller keeps the motor voltage at optimal 48 volts
But I think it would make even more sense to use an open revolt controller instead. That would shave over $1,000 off the build by itself, plus no longer needing water cooling.
Could the P&S controller do 200 amps continuous for hours?