@kumar.sachin Thank you so much for your suggestions. Here is how battery monitor function working. For key in ignition car model, Spectrum will record the battery voltage first within 0.1 second when the car is started and after that 0.1 second, the voltage Spectrum recorded is the engine voltage. That is too say, the Spectrum records battery voltage only at the beginning of 0.1 second after it is plugged. Therefore if Spectrum is plugged after your car started, at that time it will take the engine voltage as battery voltage.
In a word, to help you resolve the issue, please plug the Spectrum before starting your car.
If you have further issue, please feel free to contact us at email@example.com.