So chair starts to panic when batteries are about 11.7v
Some 11.5, some 12.
Batt volts though, depends on history before that point. Not state of charge.
But lets say 11.75.
If I just climbed a ramp or short steep hill with a 75 percent full battery that may be 11.75V.
If I drove in straight lines on flat ground,stopped to talk to someone that may be when its done 20 miles and about to stop for good.
So you cant know.
E.G while trying to start your car, when cranking, the battery can be 9V or less. It then is still 99% full. If you wait an hour some of that energy and voltage comes back. If you wait a day almost all of it does.