[HTC 10 Questions & Answers] cytherian:
Interesting -- I didn't know you could port HTC Sense software onto an LG phone. The V20 looks nice and very comparable to the HTC 10, although a bit bigger form factor than I'd like. What do you think of the hTc 10 DAC?

EDIT:

Well, I have a little bit of good news about my phone. I did a slow charge back up to 100%. I then pressed and held the volume buttons and power button simultaneously for about 2 minutes. Upon release, battery level was 89%. I charged it back up to 100% and repeated. Next battery level was 92%. Repeated, and then battery level was 97%. From there I just charged normally back to 100% and let it gradually drain down from there. When I hit 25%, I put the screen on maximum and streamed YouTube videos. The battery level began to drop about 2% after each video. I got to 17%, stopped, and rebooted. 16% and still no shutdown and boot looping. After it got below 15% I got a low battery warning, and still no shut down. At 12% it was still running.

I have a new (to me) theory that what may be happening is some kind of firmware issue, where the "adaptive" monitoring of the battery becomes flawed and thus the percentage battery level becomes misinterpreted. That's why there's that auto-shut down. Because the battery REALLY IS LOW, but the Android OS doesn't know it. And then the battery's safety circuitry kicks in and aborts power to the phone. Where it all goes wrong is when the battery becomes a bit worn after a year or so of use. The firmware starts to collect faulty battery status data and then erroneously report the battery level. THIS IS WHY, the phone tries to "boot loop" after the shutdown because it still has faulty battery data. It keeps trying, but the battery says "NO"... and denies sufficient power to complete. And then when you plug in the phone, the battery won't stop the phone from booting up because now the phone has sufficient power, so it completes. Only somehow at that moment, the firmware finally shows the right battery level. 1%.

What cemented my theory was when I plugged my phone back in to my A/C powered USB charger, but this time I did not use the Quick Charge 3.0 port. I used a normal port. And within about 30 minutes, I check the phone and it's showing a 40% power level. That's too fast. From 12%, it should take about 2~3 full hours to charge back up to 100%, and in about 1 hour with Quick Charge. What it suggests to me is that the firmware is still screwing up the battery power level interpretation.

So ultimately this problem isn't the battery. Batteries do wear down, and that's a fact. But from my observations I think it's the firmware in the HTC 10 that's screwing up in it's sensing of the actual battery power level. It gets "out of sync" and thus, this dreaded shutdown starts happening, anywhere from 20~50% power level, maybe more. It may be the micro code in the kernel... which is why some people who switched to a different kernel aren't suffering this problem.

EDIT: By the way, I've been able to consistently repeat the charging issue. When the screen reported 100%, I pressed and held the 3 buttons to boot loop the phone about 4 times (not a full 2 minutes) and after I let go with the phone in a power-off state, the battery percent jumped down to 89%. So, it may just come down to this little extra effort in the full charging of the phone. A bit of an inconvenience... but I'd rather do this than have to replace the battery at this point.