When the brakes are applied, the captured energy is used to provide extra charge to the battery. Applying the breaks on a downhill can refill around 30 to 40 percent of the energy required to get you back up.

It's worth noting that when the battery is at full charge, braking will cause the battery to spend energy to slow down. Once the battery is drained to about 95% of the charge, the regenerative breaking will again start working to fill up the battery.