Understanding why the two batteries degrade differently
Different duty cycles produce different wear patterns
An EV battery experiences variable temperature exposure from driving in different weather conditions, deeper discharge cycles from longer trips, and occasional high-current fast charging events, all of which accelerate chemical wear inside the battery cells. A dedicated home battery, by contrast, typically operates in a more temperature-controlled indoor or garage environment with a more predictable daily charge-and-discharge pattern tied to solar production and evening use.
Why this doesn't necessarily mean an EV battery ages poorly
Even with a somewhat faster degradation rate than a home battery, most EV batteries are engineered with significant margin, meaning a 79% retention figure after 10 years still typically provides more than enough range for the vast majority of daily driving needs. Manufacturer warranties, an area the Department of Energy tracks, reinforce this by guaranteeing a minimum capacity retention threshold, often 70% or higher, through a specified number of years or miles.
Degradation curves aren't perfectly linear in reality
This calculator applies a flat annual degradation percentage for simplicity, but real-world battery degradation research for both EVs and home batteries commonly shows a somewhat steeper decline in the first year or two, followed by a more gradual, slower decline in subsequent years. The flat-rate model here gives a reasonable approximation for planning purposes, though actual year-by-year figures may differ somewhat from this simplified curve.
What this comparison is and isn't useful for
This tool is useful for understanding the general difference in expected long-term capacity retention between these two battery types, which can inform expectations when planning either an EV purchase or a whole home backup investment. It's not intended to replace manufacturer specifications or warranty terms, which should always be the authoritative source for any specific product's guaranteed performance.
Following up on this result
If you're weighing V2H equipment that uses the EV's own battery for home backup, check the V2H battery replacement value calculator to see how degradation over time might affect that comparison specifically. A related check worth running: the battery capacity fade projection tool.