I was aware of most of that, except for the thresholds, so that's good to know. Checking the history, it stops at last Friday night @9pm. Was at 12.1v there, the last 2 morning starts (Monday and today) were 11.9v, so right around that mark you mentioned. The strange event I saw, isn't reflected in the graph, so the timeline is pretty strange. The confusing part was, during the 25 minute commute, the monitor never appeared to come online, as I left my phone open in the app the whole drive. It's a mystery
When I get some free time this weekend, I'll dig around and find my alligator clamp leads for my meter and do some checking for a parasitic draw.
After taking my battery out of the Sierra, charging it to float, and then letting it self-discharge, I can see that it discharges to the point where it needs a recharge
much more slowly than when in the truck & connected. So I've got some type of parasitic drain, too. I always bad-mouthed the Wally World battery (their best FLA) but I've got proof now that the truck helps drain it (a lot) quicker.
The thing was, my first Sierra did it, too (which is why I always suspected the WM batteries were at fault -- I ran the same model in both trucks, and replaced both, too.)
Once I get the Sierra back in the garage, I'll be looking to isolate where mine is (and MRRSM made a post awhile back about tracking them down, so I've got that open in a new tab, just waiting for me to jump into the job). My top candidates are the DDM and the keyless entry / security system, along with the OnStar module that's still in the truck, as those are all known battery killers.
I have an AGM in the Envoy, and it does drain much more slowly, as AGMs are advertised to do. If you find out yours is marginal, I'd recommend the AGM, myself, just for peace of mind. After the 'full replacement' warranty is up on the Sierra's Walmart FLA battery, I'll probably get another AGM for that truck (or two, as I'm thinking about a dual-battery conversion).
I got the AGM for the Envoy (edit: Duracell) at Batteries Plus Bulbs (or whatever they call themselves this month.) When I got mine, I saved $ by buying it online, then picking up at the store, so check out their website, if you go that way. They were the cheapest (non-Walmart) option, when I got mine a couple of years ago, and they have a full 5yr warranty (non-prorated).