I bought my Energi in Feb 2013 and it now has about 30,000 miles on it, all in Arizona. EV driving has dropped to about 16-17 miles from the original 22-25, and sometimes is lower with A/C use. A big disappointment but such is the life of an early-adopter.
Unless it was $200 I can't see a economic justification for replacing the HV battery.