2006 GMC Denali starting issue.

A neighbor just bought this 2006 GMC from a car dealer.

All was good for a couple weeks and then it wouldn't start. AAA jumped it once and I personally did 2 times.
First stop at the dealer they put a new battery in. It was good for 3 or 4 days, then I had to jump it again.
The driver doesn't know cars at all and was told it was a kill switch someone put in that was draining the battery. You could hear the kill switch alarm recycling at every jump start.
The car didn't start again but this time it wouldn't take a jump, by me and AAA.
Was towed again for the 3rd time and the owner was told it was a condenser/capacitor?? I asked the owner to what exactly it was and he just showed me with his hands the basic size of it and said it had wires and fuse looking things in it.
His words, not mine from what the mechanic showed him. He has no clue to where this part came from. I guess the wires were cleaned for now. The dealer cannot find what ever the heck the part is and I really don't want getting involved but just to say they are searching junkyards.
I guess he was told the kill switch was from the factory and not the issue.

Anyone have any clues? Also trying to tell this owner about parts availability with covid is stressing the heck out of him. I tried telling him to think of what garage owners are going through.

 

Could it be the RVC? Those have a ‘smart’ voltage regulator and battery current sensor, I think under the battery. They can cause fluctuation problems; maybe it’s failing?
Patrick

 

I had to look RVC up. One said rear view camera's and another sight mentioned a high techish communication or location sensor.
Could just be it has rear cameras being a 2006.
The owner just showed me his hands describing the size and it was about the size of square softball
Would the fluctuation cause a dead battery? plus no connection with the new battery after it was replaced?

 

I don’t know much about it and, other than the fluctuations, there’s not much on the web about it. RockAuto lists a Voltage Sensor that encircles a battety cable. They don’t show the module thingy, which may mean it’s not on that model or it is/was dealer only. I would imagine a failure in the system could kill a battery but don’t know if it would tell the BCM not to start, too.
Patrick

Here’s a write up of the system-sounds like it wouldn’t affect cranking.
https://www.motor.com/magazine-summary/are-you-smarter-than-a-smart-charging-system/

 

Thanks for the link.. Has some good info starting from the early days.
I'm curious to why they can't find whatever part the owner is trying to tell me is from the covid situation..