Old exhaust is out. I removed the entire thing, up to the cat. Made cutting the broken flange off much easier. Also moved some of the furniture out by giving it to my mother. Going to take a breather now and cool off for a bit.
Battery is at 12.33v, which is exactly 0.25v below the prior reading of 12.58v.
Now, while this is below 12.4v-12.6v (the recommended range), it does not necessarily signal an issue.
I had stalled 5 times in a row when the exhaust blew off. The drive home after starting it 6 times in a row is only 1.2 miles. That is likely not long enough for the car to charge itself.
Regardless, the battery would currently only be 0.07v below recommended operating range. So even IF the repeated restarts weren't the cause, I'd consider it fine.
However, I'm like 99.99999995% certain that if I just drive it 5 miles, it'll charge back to the appropriate level. Because starting the car takes a lot out of the battery, and repeat stalls followed by starts definitely will drain it. And that short drive home, absolutely, isn't enough time to charge it up.
And normally, after 3 days of being idle, it'd be below 12v given prior experience. So at the very least, there is a dramatic improvement in idle drain.
However, once the exhaust is installed, I will be unable to start the vehicle for 24 hours, as 2 of the 3 flanges will be sealed with muffler cement, which has a 24 hour curing time before you can submit it to pressure. It can be subjected to heat at any point during the cure, but starting the car would submit it to both high pressure and high heat. So i won't be driving it at all tomorrow until at least 10PM.