Is there such thing as the SBC draining battery while car is off ??!

 

I don't know for sure so hopefully someone will pop in with a definitive answer. I do know SBC likes to activate itself. If I walk past my SL with the key fob in my pocket, I will hear what I think is the SBC pump. Same thing if a door is opened. It seems like over time this could drain a battery especially if the battery is getting old.

 

SBC takes power from smaller battery, so I would believe there is no way for it to drain main battery.
It comes on for few seconds when the pressure is low and you activate it by opening the door or pressing the remote.

 

Can the SBC be running on its own on while car is off ?

 

You would hear it, if it did. However, highly unlikely.

 

My SBC is quiet enough that I will not hear it unless the car is in garage and nobody drives on the street.
Once again, the SBC should not start on its own when the car is asleep.
You have to act as I said above to start the program.
Per my observation it runs the brakes with each door opening, but it might be taking pressure from reservoir without starting the pump.

 

That is completely incorrect.

 

Incorrect as well, sbc does self tests after vehicle is shut off. Your "can" is still awake as well during this process. It is possibly it could be draining your battery but what led you to this view?