Sorry I'm not more helpful but without the proper scan tool to actually see where the issue is I wouldn't have you start testing on the system like I could. The codes in the system can provide a good starting point.
Do have a related question, you said you had the battery changed? Which battery? Your vehicle has a total of 4. There is one under the hood that is just the starting battery. Then there are the hybrid battery cassettes in the 36 volt system themselves. You might want to run your VIN number to see if those were replaced under the recall GM had for them cracking. Plus there was another one for the greenline versions that also was hybrid battery replacement for 8 years/100K miles.
You might want to call GM customer service and talk to them about your concerns and see if they would help you as a goodwill gesture. 1-866-522-9559
Sunday, March 24th, 2019 AT 2:17 PM