It's been a long journey, but my laptop is officially dead as far as I'm concerned. I'll try to summarize.
I ordered a new third party battery online. It was DOA.
I emailed ASUS and they said I could only get a new OEM battery from an authorized service center.
I took my laptop to the only service center where I'm at and went round and round with them about getting a new battery. (They said it was the system board but had no real evidence of such, especially since nothing really happened and they couldn't tell me for sure if it should run without a battery. The tech was inexperienced and totally the opposite of reassuring (in the skillsets dept.), but accommodating and friendly. They also lost about six screws in my laptop shell. I literally would need to scavenge screws or buy new ones if I'd got it working again.) They finally ordered a new battery and it was DOA. Because the laptop is older than 5 years, there are no more available to buy. In the end, it was a blessing. For the record, ASUS wants more for a new system board than I paid new for the laptop. The ASUS service center had also ordered a "test" system board, even though they knew I wasn't going to pay for that. It was more of a verification that it was the system board. Like I said, they were accommodating and doing their best to be helpful.
While ASUS had my laptop (a month or more), I eventually went into youtube video comment sections with people having similar laptops as mine and asked if it should run without the battery. It took a little time, but there was uniformity confirmation that it should run without the battery. So, at this point I determined myself that it was the system board and went and picked up my laptop from the service center.
In the following months, I watched tens of hours of laptop system board fix-it videos and ordered a ton of equipment, partially with my battery DOA refund, and then determined the board has a short, the laptop power supply verified that too after removing and intentionally shorting one of the main power 3058m mosfets. Upon further troubleshooting, it seems the main PCH architecture has a short, and as far as I can tell, there's no fixing that. I can't even find the model number of the chips online. It's like it doesn't even exist other than on my system board.
The silver lining here is that I fixed one of my other smaller netbooks with my newly acquired board troubleshooting skills.
While I'm not blacklisting ASUS products, I think my love affair with them is over. I can't really complain since the laptop worked flawlessly for 6 years, but in my mind, being top of the line and costing a small fortune, it shouldn't be dead either (especially since my sub-$1000, more than a decade old laptops are still going strong... in subtropical, highly humid, no air conditioned environments too. To be fair, I did use the ASUS far more, but never for gaming or mining, only for Visual Studio projects and VMWare dev environments, never overheated, yearly cleaning, etc...pampered....never even close to overheating). I've never had a laptop die with no hints of doing so either. It's still just bizarre to me. However, it's not just this laptop, I recommended ASUS phones and other gadgets to all my family and friends and it hasn't really worked out well, although not terrible I suppose either. I'll still buy ASUS products though, just not blind.
Anyway, that closes this laptop chapter. Hopefully, there's some useful info in there somewhere for someone experiencing the same issue. I'm just happy to close this browser tab after eight months. 🙂