Sorry to hear about the issues with the CT6. Depending on the battery purchased, ( quality, amps, guarantee) the battery may be covered by a warranty.
however if the incorrect battery was installed, that may be the issue. Q: Does the battery take a charge and can start the car after the recharge? Also if the vehicle is not a primary rather than a drive when every, yes the battery will die, and after it is fully charged, a battery tender is suggested, a tender will not recharge your dead battery, however.
These cars rely on a significant amount of power to run the computer, lights, engine components, and the like. if the battery is truly dead, I suggest it is the re-charging system in your vehicle (alternator and the like). Replacing the battery will only delay the repair. Most car part stores will not only check the battery but also have simple diagnostic equipment to check the charging capability of the vehicle.
The most logical issues are: charging system failure, wrong battery, corrosion of terminals, something is on in the vehicle for long periods of time between using the car, or a short in the electrical system. Batteries are expensive, and diagnostics at a dealership is about $250.00. Wishing you luck in determining the issues
Dave
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