Fun little exercise. I never really thought about $/mile.
I am only considering cost per mile for fuel. I am giving no consideration for other costs. I also could have made a mistake anywhere in my thinking.
If I use the 300 miles per/month number, $0.175/mile for electricity to charge and battery replacement every 3 years at $750.
Battery cost per mile = $0.069.
($250/year, $20.83/month, $20.83/300 = .069)
Charging fees per mile = $0.0175
Quick glance tells me my electrics use about 8.69 cents per mile…
Looks like I have to get my batteries to last closer to 4 years to compete with the OP numbers based on the assumptions I have made.