None of the voltages will kill the car battery, but they will all shorten its life! The lower the voltage setting, the shorter the car battery life, assuming that it regularly reaches the cut off limit, which depends on how much and how often you drive the car.
A general guide, assuming that your car has a lead acid main battery:
- For an AGM car battery use 11.8V.
- For a Long Life (Calcium)(5 Year Warranty) battery use 12.0V.
- For a Maintenance Free (Cheap)(≤3 Year Warranty) battery use 12.2V
If you often leave the car unused for over a week at a time then it might be wise to increase that by one stop.
If you don't regularly do drives of more than 1 hour, or occasional drives of over 4 hours, then it would help battery life significantly if you used a battery charger to 100.00% fill the car battery every 3 months.