Two minutes of flight per pound of battery would be pretty amazing.
Lets do some math
4kwh is double a bit more than 8 Bonkas which would be about 40lbs as well. They have something with a slightly better density than LiPos maybe. And the claim is triple the flight time. 60minutes/38lbs or 96seconds/lb. That’s a very light pack and a really efficient motor/controller/prob setup.