What is the primary operational advantage of using an auxiliary endurance braking system (retarder / engine brake) during long mountain descents?

1. It provides wear-free continuous braking, keeping the foundation wheel brakes cool and fully effective for emergency stopping
2. It completely eliminates the need for foundation service brakes on the vehicle
3. It recharges the vehicle's 24V starter batteries through regenerative braking
4. It increases the top speed of the truck on uphill gradients