I have 2 weeks with a 2013 Energi. Car is very cool, I'd be pretty confident of getting 40Mpg with regular Cmax.
Dealer chose to jump battery the 12v battery first time I went to test drive at an indy lot in Chicago.
I can tell you that another dealer had one with 40K miles which was declared 'lemon' title,but no detailed reason shared, although a replacement battery was in the carfacts. These guys were still asking like $19 for it or something crazy, claiming they could still sell it to auction houses...
3rd party 'independent' Ford Dealer Mechanic thought my battery was 'OK' , taking a charge, noticed some slight corrosion near contacts on battery back under trunk, and it's possible it's been weakened from time at dealer lot.
I also managed to kill the battery once thus far, but I think it was because I actually left the car 'on' and left it for an hour, after it had been only driven on EV for a couple days, and I was playing with the lights, getting in and out of the car all morning.
I was able to get a jump start thankfully, I kept cables with me.
There is a bit of a trick with the jump start to make sure you are not on EV, and to rev accelerator while in park or in neutral.
My sense is that worst case the battery might need to be replaced prematurely, however I have a sense that most issues with dead battery reports could be due to 1) owners driving in EV mode all the time, not 100% clear to me that driving in EV mode and charging actually charges the low voltage battery or not in the Energi.
and/or 2) not knowing that car is still really on, leaving car. Different theories on whether engine should kick on automatically in that mode.
not sure if that helps, but other than not being able to hook up my ford mobile yet after trying every day for 2 weeks, I like the car a lot.
Mine had 90K miles (high for a 2013) , I paid $10,500. Had to put some money into 2 tires, alignment, really could have used 4 tires due to some pretty uneven tread wear, strange rumble in rear tires at lower speeds. Had to rotate to put the old tires in the back, but the new ones up front.
Opted not to do brake work yet, though will likely also need rotors when I do it due to their current thickness allegedly a bit too thin to machine again....