Like a gas - electric hybrid, it uses a lithium ion battery to assist the fuel
cell during acceleration and capture energy through regenerative braking, thus improving fuel efficiency.
Charge - depleting mode allows a fully charged PHEV to operate exclusively (or depending on the vehicle, almost exclusively, except
during hard
acceleration) on electric power until its battery state of charge is depleted to a predetermined level, at which time the vehicle's internal combustion engine or fuel
cell will be engaged.