Justin;
Why the 3 min pit stops?
Just have it where every one has to stop every 10 min, change a battery and then get back to racing. This way if you can pit faster than someone else you could make up some lost time/laps.
Limiting it to a 3min pit stop just makes the enduro 6-10min races.
This could lead to some inovated battery setups.
Just my thoughts
Bob Oaks