I'm still on the OEM battery in my 2016.5 and it's still doing its thing, no issues.
I've used a battery tender, religiously, for its entire life though...
I have no idea what a 'freedom flyover state' is, neither does my web search engine it seems, but what does that have to do with the use of alcohol in premium?
Most agricultural (CORN) states mandate the use in our gas. Non-alcohol gas can still be had but normally it cost more and is harder...
If it makes you feel better then go on.
Nothing wrong with using Premium when not required (other than costs) but don't think for one second that Premium does a better job at managing water than the lower octanes.
Are you using non alcohol Premium? You sure?
Improve in 5 years? Don't you have that backwards?
Keep in mind that JustThisGuy has a 2l engine with a manual trans. That most likely means that he's not in the USA and could possibly be using the Imperial gallon, which is 20% larger than the gallon we use here in the USA.
If you're suspecting the gas, you might want to wait until you fill up again before doing all kinds of troubleshooting, could be wasting your time.
I have the same CX and it's also been flawless to this point. Never used premium though.
I hope that you mean that your last oil change was 4,500 miles ago and not over 21,000 miles ago?
Have you checked the oil during this interval?
Did you check the oil right after the dealer did the work?
The system doesn't care if the tires are unevenly pressurized. Once you press the reset button the system now looks for any deviation in what the pressure was at that point. The system looks for any changes, not what the pressure actually is.
Have you checked your owner's manual? Surprisingly, this info is there.
Your 2016 does not have individual pressure sensors for each tire, and certainly not for the spare.
"I read here that sensing is done via differential rotation speed sensed by the ABS."
^^^^^^ This.