2020 F350 6.7 weak start

[way2roll]

I bought my 2020 F350 6.7 new and I've put about 28k on it. I haven't had a single issue with this truck until now. Sometimes the truck sits for a day or so without being used and when that happens it's a "weak" start. It always starts (knock on wood) but the last thing I want is to be on a trip pulling the FW and it doesn't start. There is no code. It has 2 batts and frankly I don't know how to test voltage on a 2 battery setup and voltage isn't always the best indicator anyway. And I do know, if one batt is bad it drags down the other. I've also read that these trucks have had issues with the starters. It's still under warranty and I was told to make an appointment for a diagnostic test. But I trust you guys more than I trust a dealership and thought I'd throw it out there to get your thoughts so they don't brush me off. Also been noticing intermittent hard shifts into 3rd on a slight grade. Again no code, but I have heard there have been issues with these tranny's and intermittent hard shifting. I plan on asking them about it, but again, always worry about an honest opinion from the dealership. They always seem to find stuff when the warranty is over, but funny how they can't find the issues when it's covered.

[Grit_dog]

So it cranks slower after sitting for only a day, but cranks faster if started within the same day as it was run last?
If that's the case, it is not the starter, it is the batteries.
If you dont want to test them, and suspect bad battery/power draw, just let it sit for a few days and see if it's worse than 1 day. Otherwise, check battery voltage of each battery separately and/or have them load tested.

That's where I'd start (no pun intended, lol)

[ksss]

It could be the batteries or you could have a parasitic draw somewhere that draws down the batteries as it sits.

[4x4ord]

If I was going to check the batteries I'd unhook the negative terminals on both batteries after parking it. A couple days later I'd check each battery individually. They should read 12.8 volts. My 2011 had its batteries replaced under warranty at just under 3 years old. It would only crank momentarily and if it didn't start the computer would cause the starter to cut out due to low voltage.