No one knows yet how this system will react with regard to your question. I can say that in the Prius PHEV, as the battery lost capacity (after 5 years) the EV range decreased. Since it wasn't all that much to begin with, it only ended up being a mile or two less (but that's out of a possible 12-15), so maybe a 15% decrease. In a Clarity, that might amount to 7 miles at 15%. But we won't really know about any of this until some of the earliest buyers (last December) start hitting the 4-5 year mark. I might not have mine by then; it'll be paid for in two more years.