KESS V2 Red pcb battery voltage

[Pichuks]

Hello,i recently bought the kess v2 red pcb clone,from aliexpress.
The main question is,how important is the voltahe of my battery when i do reading of ecu?
I can do successfull ID,and partial ECU reading. But when i do full reading,at the first stop where i need to swich the ignition off (about 33% of reading) i got wake up error.
The thing is,when i do ID the voltage shows about 12.7v...and when i get the error i have 12.1-12.2v. So i m thinking maybe the voltage drop is the reason for the error? I know that i need extra PSU,but at the moment i dont have one.
i m worried,that my kess device is faulty,thats why i m asking this thing.
I somewhere read that if i can do ID reading,that means the device is in working order and good,its true?
Car: BMW E61 530dA 2006

[Pichuks]

Can someone tell,if its true,that if i can do ID,that means that the unit is good?