Battery going dead and Sirius XM “Contact Onstar” message

Hello, new member here. Bought the wife a new 2021 Blazer Premier last year and have been having some issues with it I was wondering if anyone else is familiar with. Since new car has always had message come up on radio to contact onstar you would have to clear it every time the car was started. Dealer said this was normal so we just kept clearing it. Fast forward to wintertime. Car sat for a couple days and the temps got below zero, car wouldn’t start battery was stone dead. Jump started with my pickup and pulled it in our shop and fully charged the batteries. Wife used it for a couple days, then same thing dead again. Jump started and charged again, then brought to dealer. Dealer could not duplicate, but tested the battery and said it was fine. We got the car back and a few days later it was dead yet again. Brought to dealer a second time, again they could not duplicate but replaced the battery under warranty. Couple days later car went dead again, this time i left it and dealer came out and got the car. They kept car for 2 weeks, and ultimately told me they did not find a for sure fix for the issue, but did some software updates and replaced onstar module as they said that was why the message was always on the radio. Got car back in February and it has worked fine. Yesterday wife told me onstar message started coming up again every time car is started. What the heck!? My guess is the battery will be draining too but it will be easier for the car to start with these warmer temps so we might not notice unless we let car sit for several days