Can your car power your fridge?

V2X, or Vehicle-to-Everything, is a communication and electricity transfer technology. It allows vehicles to interact with and send energy out to devices and other electric systems. It can be used to enhance safety, balance energy use, and use an EV battery as portable storage. V2X is an umbrella term that encompasses many things, such as V2V (vehicle-to-vehicle), V2H (vehicle-to-home) and V2G (vehicle-to-grid). V2G, for example, allows bidirectional charging and uses batteries to support the grid. Vehicle-to-home can hook up a car battery to a smart meter to power home appliances or charge from a home solar setup. 

V2X applications can benefit EV owners (and society) by enhancing the timely use of renewable energy, shifting peak load power, and enabling participation in electricity markets (e.g. allowing owners to deliver energy back to the grid - often at a profit). However, most battery modeling has not accounted for V2X operation. As a result, there is not a lot known about how V2X will affect capacity and power fade over the lifetime of the battery. 

There are several factors that could influence degradation:

1. More Charge/Discharge Cycles: V2X involves charging and discharging the EV battery more frequently than if you’re just using it as a car. Additional cycles may accelerate the aging process.
2. Depth of Discharge (DoD): The degree to which a battery is discharged during each cycle also affects degradation. High DoD cycles typically cause more wear on the battery, so frequently using the entire battery to power a home or appliance may cause aging more than if you just use a small percentage of the battery capacity.
3. Temperature Effects: Repeated cycling and high power flows can increase the battery's operating temperature, which can contribute to accelerated aging. A well functioning BMS should manage this risk, although it will add wear and tear to the BMS.
4. Battery Management Systems (BMS): Modern EVs are equipped with advanced BMS that regulate charging and discharging processes to minimize degradation. V2X operations must be well-integrated with the BMS to reduce the impact on battery health. For instance, the Kia EV6 has V2X capabilities, but warns that certain high voltage appliances may exceed the power draw that the battery can provide. 

What it comes down to is that the overall impact on degradation depends on how often V2X is used and in what capacity. Occasional use with shallow discharge might have a minimal impact, whereas frequent and deep discharges could accelerate wear more noticeably.

A study in May 2024 sought to investigate the effect of V2X on batteries by developing a comprehensive model to simulate different types of V2X use to assess their impact on battery health. It combines real-world EV data and battery testing with charge and discharge cycles derived from actual EV operation. This study determined that the V2X scenario resulted in greater battery degradation (~3% of 20 months), but that this increased degradation was less  than the amount that two cells may differ as a result of manufacturing variation. The researchers concluded that adopting V2X applications does not significantly increase battery degradation and, if run carefully and in a controlled fashion, may even reduce capacity loss.

Similarly, a study published in April 2023 indicated that the average car-only battery degradation was about 1.5% per year, resulting in 15% battery capacity degradation over a 10 year period. Including the battery for V2G, one of the key V2X applications, added 1.8% degradation per year. This was mostly consistent with the findings from the May 2024 study (3% over 20 months). Over 10 years, a 33% capacity decrease would be expected, leaving 67% of the battery accessible for post-mobility use. 

An important caveat for this second study is that researchers used a PHEV, which has a relatively small battery (~16 kWh). They used 8 kWh, or 50% of the total SOC, for the V2X testing. If a similar experiment were repeated with a larger battery, for which 8kWh is a much smaller percent of total capacity, there would likely be even less degradation. 

A key strategy to minimize V2X-associated degradation is advancements to the BMS that can continually monitor, predict, and optimize battery health using age, previous usage, and anticipated needs. For example, the BMS could be programmed to limit V2X use in high heat, or when the SOC is low. 

The takeaway is that V2X use will usually result in faster battery capacity reduction due to the extra cycling. However, the total amount of degradation is relatively small, assuming the use is similar magnitude to normal EV use. Power levels required for residential grid services when using V2G, for example, are relatively benign and unlikely to exceed the battery’s healthy output range. As the power demand and total SOC range used increases, it’s likely that degradation will increase proportionately.