Originally Posted by -Ray-
Read post #4.
September 2016 I worked on my brother-in-law's 2004 Envoy. His problem? Without fail, the battery would go dead after sitting after 18 hours. I used a DC Amprobe that I clamped around the positive side of the battery cable. Some use a volt meter?
He had already installed a new battery, alternator, starter, and some window switch a local GMC Dealer said he needed.
After checking several potential problems, I found nothing until I removed the after market radio. Once the radio was removed, the parasitic drain disappeared!
Why a aftermarket radio drains the battery in these vehicles? I can't tell you? However, I did use the search button on this site plugging in "parasitic drain" and found this particular problem (among others) is more common than many may think (including myself). It's been about 1-1/2 months since doing this. Now the battery stays charged like it should.
It may not be much of an answer? I hope it helps in some way. And you're able to locate your problem. I understand additions like remote start, aftermarket radios, Bluetooth and such can and often do cause a host of problems?