iPad will not turn on after charging for multiple days, showing dead battery symbol

I have had a 6th generation iPad (Model A1893) for a few years now, if not since it was new. I started to notice that the battery would deplete quickly, within a few hours of regular use. Last Wednesday, I found that my device had completely died, only showing the screen that the battery is dead, please charge the device. I plugged the iPad in, and left it alone. I went back to it a few hours later to find that the device was charging, but it only showed the battery symbol with a slim red line towards the bottom of the battery.

The iPad recognizes whether it is plugged into a power source, but does not seem to have enough power to turn on, even when it is plugged directly into the wall outlet with the original wall adapter. At this point, I tried several different chargers and wall adapters, some being Apple products, others being 3rd party cables with MFi certifications.

I left my iPad plugged in for the rest of the day Wednesday, all day Thursday, and into Friday. The device never got warm, and never powered on. Friday afternoon, I unplugged the iPad, put it back in its original box, and put it on my shelf.

Friday evening, I took it back out of the box to find the model number and serial number, the iPad was on and charged to 100%! I was able to use it as normal, with all of my apps, documents, settings, and information present, as if nothing had happened. Figuring that the iPad was back to normal and fully charged, I left it on my nightstand for the rest of the evening, not charging. Saturday morning comes, and I am back where I started. iPad is dead, knows that it is plugged in and charging, but will not power on. Frustrated, I left it plugged in and went about my day.

Now, as of writing this, it is Sunday. I did some research on tips to restart and/or power on a device that is unresponsive. I tried hard restarting the iPad by holding the power button and the home button for over a minute, just to find the dead battery screen cycling, with no difference whether the device was plugged in. I then tried putting the iPad into "DFU mode" by plugging the iPad into my computer while performing a series of button inputs on the iPad. I got iTunes to recognize the device, and that it was in recovery mode. iTunes prompted me to restore the iPad and download the newest firmware onto it, so I did just that (I perform regular device back-ups, so I was not worried about losing any data). The Apple logo appeared on the iPad with a progress bar underneath it, and I let iTunes do its thing. The device restoration completed, and iTunes said to wait for the device to power cycle back on so that I could start the process of signing into the iPad as a new device. Without hesitation, the iPad went back to showing a dead battery symbol, and that's how it has been since.

Just a footnote, my iPad never got warm while charging over these last few days, and has never shown any sign of pressure against the screen that would indicate a swollen battery, which I have dealt with in the past on other devices.

Sorry that this is so long winded, but I wanted to make sure that I got my timeline out, with any/all attempts at solving this issue I had made. If anyone has any suggestions, that would be greatly appreciated, as I have gotten a quote for upwards of $200 for service on my iPad from Best Buy and a third party repairman, with no guarantee from either that the device will be functional after service.