This is what the B mode is
This is what the B mode is for. The owner's manual doesn't state anything about enhanced regen in B mode, so reading this article had me thinking the author was a tad confused. What it does do is take electricity directly generated from the wheels and use it to spin the combustion engine with the throttle closed which creates resistance simulating engine braking in a car with a mechanical trasmission. The prius has two electric motors. One is connected to the wheels, and the other to the engine. This disperses the potential energy of going down the hill into engine heat which is then taken care of by the car's cooling system which can handle much more energy than a car's disk brakes. B mode is designed for long hill descents where you would normally need a lower gear in a manual or automatic, or a compression brake in a truck to avoid overheating the brakes. It should actually rob you of regen energy since you're turning kinetic energy into heat instead of voltage.