Vehicle batteries are known to lose capacity with time and cycling, and prior research has commonly assumed that EV batteries will provide useful life within EVs down to 70-80% remaining energy storage capacity. Around this level of remaining capacity, it is assumed that EV batteries must be retired because they will no longer meet the range and mobility needs of drivers. Many studies have proposed that after retirement from their vehicle lifetime, vehicle batteries can enter a second life where they serve as stationary energy storage for the electricity grid.

A new V2G-Sim case study quantitatively examines the assumption of having to retire EV batteries from vehicles once they reach 70-80% remaining capacity. Driving patterns from drivers across the United States are simulated in V2G-Sim within vehicles that have experienced different levels of battery degradation. Battery SOC profiles from these simulated vehicles are examined to identify if drivers run out of charge during their trips, and to determine how much range drivers would have if they needed to make an unexpected trip.

The results from this case study show that EV batteries continue to meet the needs of a vast majority of drivers well beyond degradation levels of 70-80% remaining capacity. These results suggest that battery degradation may be an over-emphasized concern in terms of meeting the mobility needs of drivers. EV batteries may well continue to serve the needs of drivers for at least as long as the lifetime of the entire vehicle. These results also challenge the assumptions of a majority of battery second life economic analysis literature because it is shown that batteries entering their second life for grid storage may have much less than 70-80% remaining capacity.