OK looks like its time for me to clarify some stuff for you.
1) Hold the left OK button and power up the car with your foot on the brake as normal. KEEP holding the OK button for several seconds, about as long as it takes for the 4 beeps to stop (no seatbelt on) and you will see ET in the left box. At that point you can look through several new screens, one showing the battery under charge at 14.0v on mine (I just did this) and your RAFE, running average fuel efficiency of the ICE, an interesting item to see. If you multiply this number by 14, when you fill the gas tank, that's the range you will get on gas.
2) There are 3 meters, none are lifetime summary meters in a 2013 model. The first one, I call the "outside meter" is the one you see showing 71.6 in all the screens that you scroll through on the left side, empower, enlighten, etc. You can reset that at any time, its independent of the others.
2a) Then there is trip meter 1, it has its own mpg reading tallied separate from the outside meter.
2b) Then there is trip meter 2, it has its own mpg reading tallied separate from the outside meter.
2c) And finally on a 2013 model if you're lucky enough to have the OEM one not hacked by Ford, there is the Lifetime summary meter shown after the trip meter AFTER you power off the car. Those two are separate from the rest, and you can reset the lifetime summary meter is a separate screen in the left side.
SO, what's with all the meters? Well the lifetime summary shows my lifetime car average, say 68mpg. The trip 2 meter shows my this year car average, say 78mpg so far this year plus gas burned. Trip1 meter shows any trip I take throughout the year performance and fuel burned, and the "outside meter" I use to reset the most often, to show my current burn average, so either in EV mode or when I get on the highway to see the ICE performance. Don't use the outside meter for lifetime summary, that the one that should be used most frequently to check how the car is doing say at 55mph vs 65mph vs 75mph on the highway at 1/2 hour intervals for example, or for every 1 gallon burned, or whatever you choose.
I'm not worried about my 12v battery, even at 12.26v. You don't need to worry unless you start dropping voltage below 40% charge level, or less than 11.9v then you're in the yellow, anything above 11.9 you're in the green for battery life.
Try doing exactly what I said above again, you should for sure get into ET mode, many other people besides me have done it.