after changing the battery on my '21 f150 Lariat i got a "service engine soon" and a "shift system fault". Everything functions as it should, how do I correct this?
Battery reset procedure did not correct the problem. Still showing error

 

1) fully charge the battery outside of your truck with a trickle charger before installing

2) reset the battery management system (BMS) per the procedure below:

Turn the ignition on without starting the motor, flash your brights 5 times, then mash the brakes 3 times. Watch the battery icon in the dash until you see it flash 2-3 times, then turn the truck off.

 

@Neversummer is absolutely correct.
Besides, our glorious trucks are designed with even more glorious computers that will throw an error code without any real issue just because 12V line voltage drops below the threshold.

 

My 02 Vette will do the same thing if the voltage gets too low. All modern cars need a certain voltage to operate all systems correctly. This is not unique to Ford or even to vehicles, it is unique to electrical systems period.

 

Yep, our F-150s seem to display the same type of strange low battery issues like my C6 does. A prime example is both of mine have had a single headlight on while just sitting.