Control module voltage is one of the OBD PID. It signifies the car battery voltage. Is there any way to calculate how much current is drawn in a drive (say 7 km from my office to home). The voltage will keep on decreasing, increasing in this drive, but I am interested to calculate how my current (or rate of current) is being drawn during discharging of the car battery. The calculation would involve using OBD PIDs (most preferably the generic Mode 01 PIDs).
The notion that battery voltage will reduce while driving is incorrect.
All modern production vehicles will boast alternator acting as a electrical generator to maintain battery voltage. The battery cannot sustain sufficient charge for even an hour in the absence of a charging issue.
As such, control module voltage will remain steady during normal operation and cannot be used to perform any kind of electrical energy consumption calculation.
On some vehicles you can monitor duty cycle on time of the alternator control circuit or alternator load. Both are usually an on/off signal that will give you a percentage. Some flaws in this are something like A/C on will cause 100% whether needed or not and hard acceleration ( like going uphill ) the car will disable the alternator 0% to give you more engine horsepower ( the alternator is a load on the engine ).