First off I just want to thank all that have posted on this subject, over and over again. I have been researching this site for days. Bill Curlee and his post have been very helpful and without his post I would have been lost. I have had 3 Vettes, two C4's and the third one a used C5 I purchased over a month ago. I have never messed with the C5 in any shape or form so figuring out it's little problems has been a huge learning experience.
I am a truck driver and I am usually gone a week at a time. When I bought the car it had a Red Top Optima installed and it would be totally dead after 5 or 6 days. I also noticed when I would drive it the flux in volts would be 12.5 to 14 and I was getting a low voltage code on a Rear O2 sensor. I pulled the Red Top and charged it up. It would never break 12.5 and would be at 11.0 overnight. I am not to impressed with Optima and so I replaced it with a good battery. I then started looking for a Battery drain.
The person that owned the car before me also removed the stock Bose System and installed an aftermarket Kenwood system. I check for system draw and it was very high well over 100 Milli amps. I cleaned all my grounds, checked the alternator, power seats, rear defogger. I also found that number 7 spark plug wire was not even connected to spark plug. It was on but not clipped to plug. Everything checked out ok, yet I was still getting the draw. I then went to fuse box and started pulling fuses. I remember reading in Bill's post about the Bose amp staying powered up. I also noticed the Bose Fuse #28 was still installed. So I pulled the fuse and it looks like it has stopped the Battery Drain. My Stereo/Navigation runs and sounds the same, so obviously it has been rewired to exclude the Bose. After pulling the fuse and putting it all back together I took it for a spin. My Volts now read a constant 14 and the Low voltage O2 sensor code did not pop up. It's still to early to tell if this is the definite issue, but it's looking promising. I parked and locked the car and got a reading of 12.85 at battery, it has never read that high. I was actually getting 12.2 to 12.0 reading after 24 hours of sitting before pulling the Bose Fuse. I will keep checking through the day and see if there is a drop.
Just wanted to tell my story of Battery drain thank all those particularly Bill Curlee that have posted on subject.
Will let ya know if problem is resolved. .........ah my addiction to Plastic Cars!