2020 GC "Stop/Start Disabled. Service Stop/Start System" after main battery change

[RePete222]

Hello, I changed the main battery in my 2020 GC Limited earlier this week (did not change auxiliary ("sidecar") battery). Now I'm getting the message "Stop/Start Unavailable. Service Stop/Start System", and a yellow light on the dash consisting of the Stop/Start icon with an exclamation point next to it, every time I start the engine.

Is it possible that the aux battery also needs to be replaced? Would that be a possible cause of this message? Turning off the stop/start system with the console button doesn't make the yellow light go away.

Having changed the main battery in a VERY COLD garage (outside temps were in the subzero teens), I'm planning to wait for warmer weather here in Omaha before dealing with the aux battery.

Thanks