My 2019 nissan altima car battery voltage is 11.9 volts when the car is off. Used a battery tester to test the charger which is working. Battery always stays at 11.9 when the car is off. With exception of surface voltage which drops to 11.9 shortly after turning the car off. The car has no problem starting. Should I replace the battery which is only 2 years old?
That voltage is way too low. You may have a charging problem. Take it to your dealer. Some or all of this may be covered by your warranty.
I’d guess your voltmeter is not accurate, at 11.9 volts you wouldn’t be able to start the car.
I second the opinion about a bad voltmeter. Try it on another car, or on a 9v battery.