Batteries in my 2017 (built 9/22/2017) finally went out this weekend.
Last week I had an issue when the truck was started, and it popped up several odd errors, Service Advanctrac, Stability Control Not Available, and something about the rear parking sensors (Do not remember the exact msg). I was able to shut off the truck and restart with no errors.
This weekend, I whet to start the truck and had nothing. No dome light, radio, or anything. I was able to track down a pair of Motorcraft Group 65, 850 Amp (Up from the factory 750) for a bit over 2 bills each (ouch). Brought them home and installed them. Had lights and radio as soon as they were installed, but no crank, and no gear indicator (PRNDM). Tried multiple BCM resets without luck. Finally made an appointment with the local dealer, and called AAA to have it towed. When the tow truck arrived, they asked me to put in in neutral to load it. When I got in, I noticed I has the gear indicator, so I thought I would try it. I did and it started. I am not sure if there is an anti-theft system that requires a long reset after the battery is replaced or what, but it was just strange.

I thought I would post this in case it is helpful to anyone else. Here in a few weeks I will be replacing the factory tires. This will be another large OUCH moment.

 

I believe that some people have had that issue, where after swapping the batteries the truck needs some time (sometimes up to 8 hours?) to properly reset itself. It can't hurt to have the dealer check it if you don't mind paying for the diagnostic fee.

 

Thankfully it was only a 45 minute to an hour wait for the 'reset'. Was the first time I have seen a need wait after a replacement. Too many computers on these things.

 

Did you pull both old batteries at the same time to put the new ones in?

 

I think that I can see where you're going here. If leaving one battery connected is the "answer", how then would you change out a single battery on a gasser and not have the op's issue?
Changing batteries on my 6.7 Cummins was always a potential sparkfest if I didn't at least disconnect both positive leads when I started.

 

Yes, both were around 11.5volts, and were replaced together.

 

Reason I asked was that if you only take one out at a time, and put the new one in, then the truck never loses voltage, so its system stays live during the replacement, keeps the issue you had from happening.

Also, just so you know in the future, battery voltage doesn't tell the story on battery health, only charge level.

 

I replaced both oem batteries with AGM batteries on my 2019 6.7 at the same time . After snugging down the post clamps I installed the battery hold downs . Jumped in and started it up . There was never any delay or any problems with everything loading properly . Let it run for a minute or so and drove for about 15 minutes . I'm not sure why his truck had a long delay .

 

There is a reset for replacing batteries, at least on 2020+, they had to do it on mine when they replaced the batteries, hooked up the scan tool to do the reset.
My thought is that if the voltage is not completely disconnected by removing both batteries at the same time, you could get around that.

 

There us a handy little tool that plugs into the "cigarette" aka power port that delivers 12vdc so the vehicle doesn't lose power. Not sure if that will work on a newer vehicle that has a BCM that controls everything

Easy enough to clamp a couple of wires onto the battery cables and connect the other ends of the wires to a spare battery

 

It is possible that mine sat with dead batteries for up to a week. It may be that the computers have capacitors that are able to maintain them through a short outage for a swap.

 

Just completed battery replacement and was similarly concerned about a "spark-fest." Those cables are thick and set in shape so they resist staying tucked safely out of the way. I used a short bungee cord attached to the hood catch to hold the hot/positive cables out of the way while i disconnected, removed and replaced/reconnected each battery one at a time.