Here's a quick how to video that I made showing replacing the stock 12v 45AH lead acid battery with a 12v 70AH AGM battery.
Some folks have had issues with the stock 12v battery running down and not being able to unlock the vehicle, or start it by remote, or some to even start it at all, as it is needed to engage the relays for the high voltage battery. Some also get the "Deep Sleep" message in the FordPass app that indicates a low battery voltage for the 12v battery.
Adding a larger AGM battery helps to prevent these issues.
Besides topping up the AGM battery prior to install, it took about 20 minutes.
Edit - The 12 volt battery is under the floor in the rear cargo area. In the Titanium hybrid, the spare tire covers it, so remove the spare tire to see it. In the SE hybrid, there is no spare tire, so you'll see it once you lift up the floor of the rear cargo area. - Edit
Here is the battery that I used because I found one for $125! https://www.amazon.com/gp/product/B008FWCLHU
But any Group 48 AGM 12 volt battery will work.
Edit 2 - Thanks to a tip, I checked with the Ford service department and they said they do need to update the programming for an AGM battery. - Edit 2
Edit 3 - If you want to keep it all Ford, or have the dealer do it, here is the Ford battery:
Part #: BAGM48H6760 (48H6)
- Edit 3