F150: Help me diagnose my “no-start”

Hi, the patient is a 2018 F150 with the 5L and 10 speed transmission, mIleage is around 110K kilometres (~70K miles):

The truck is used to pull our travel trailer and as an occasional 2nd vehicle. So lately it has seen limited use. I'm in the Ottawa area, the outdoor temperature is just below freezing and the truck stays outside.  After a short trip today, it didn't want to start after a trip to the mall. I was able to get it back home after waiting a while in the parking lot - it fired up on probably my 3rd or 4th attempt to start. 
So I made it home and shut it off. Checked with a digital multimeter and the battery showed 11V. I was able to restart and checking the battery at idle, it was alternating between 13 and 14V. 

I'm assuming I need a new battery and nothing more. Since I'm getting 13+ volts at idle I'm guessing the alternator is OK?
 

Would you agree with the diagnosis?
 

Thanks, Paul 

Any codes? Your diagnosis seems right. Is it the original battery? Now days with the computers you get about 4 years from a battery. So if it's the original, you're due.  13 to 14 volts at idle is where it should be. 

With 11 volts and freezing temps, I am amazed you got to start at all...

Hey, thanks for the reply. No codes present. 
Sorry for the delay, I was unexpectedly away for a few days and lost track of my post. I forgot to mention this is an AGM style of battery- I thought I'd get more than 4 years out of it, but you're correct that with all the electronics and Start/Stop, that it's most likely the issue. 
 

Cheers, Paul