You may select according to your needs.
When you choose the lower level 11.8V/23.6V, you could get a longer parking recording time.
If you are worried about draining your car battery, the highest level 12.4V/24.8V is your safe choice.
Here we will take 11.8V/23.6V as an example.
Generally, the voltage of the car after starting is between 13.2V -14.5V, and it will drop to about 12.2V after the flameout (depending on the model).
To avoid draining your car battery, a protection voltage of 11.8V can be set. so when the battery voltage drops to lower than 11.8V, the power will be cut off and the cam will stop recording.
For those cars whose voltage is around 24V, 23.6V is the best choice,