It will still get much better mpg even with lower quality batteries. Also for the record I'm driving a 13 year old electric car and while it only had a 70 mile range at release, I still generally get about 50 to 60 miles on a charge.

I have a 2013 Kia optima hybrid that gets 550+ miles per tank; in comparison my kia Sportage gets >300. I filled that up weekly because I couldn't go 2 weeks without out going empty. My hybrid I've had for a year has had less than two handfuls of fillups; basically I go over a month without filling the tank (they're similar size tanks)

The mpg I average is pretty low because my commute is short and on surface streets so it's roughly 35mpg but on longer trips it goes above 40mpg. The Sportage was rated for 21/28 but it hardly ever got that high

Even if it has reduced capacity due to age, like the other comment said, it is still vastly more efficient