How do I convince Apple support that my iPad battery failed?

I have a 1st gen iPad Pro 12.9". It's 4.5 years old. A week ago it started repeatedly rebooting about two minutes after boot. When booted it shows battery at 3% or 4% but once showed it at 100% (though it still shut down after a minute or two).

Apple tells me that for iPads they don't actually replace your battery. It's too hard because the screen is glued on. Instead they swap out the whole iPad. Thus, I can't just say "Please replace the battery. Here's $99." They replied with "We have to replace the whole iPad. That will be either $99 or $599 depending on whether the problem is the battery or something else."

At the Apple store it wouldn't boot on a standard 1.5A (7.5W) charger or from a portable battery (wattage unknown). It required the 3.6A (18W) charger from an iPhone 11 Pro to boot at all. Once booted we were unable to run the diagnostic because it would power down too quickly. But we were able to go into settings and look at the log of kernel panics. The most recent panic was five days before the Apple store appointment, and the phone had shut down and rebooted at least 20 times since then, including four or five times in the Apple store. So these shutdowns were not being caused by kernel panics, which the Apple tech said they would be if this were a hardware problem, not a battery problem.

However, he ultimately declared this to be a hardware problem, not a battery problem because he said he looked in some document that said that this iPad model would draw its power directly from the charging wire, rather than the wire charging the battery and the iPad drawing from the battery. Thus, if it's plugged in and still won't stay running, the battery is not the problem.

This is a really big deal because replacing the iPad due to the battery costs $99 and replacing the iPad for any other reason costs $599. I think the tech's conclusion is wrong and it's unfair to make me pay $599 for a bad battery. How can I convince them that the battery is failing so I can get the $99 price?

• What document would the tech have read that said that about drawing power from the charging cable? Can anyone find a document to the contrary? I don't think this argument is valid because I replaced the battery of a 2013 Macbook Air. Before the battery replacement the battery had to be charged for about 10 minutes before it would boot, and then it would run all day while plugged in. So even though it was drawing its power generally from the cord it still required some amount of functioning battery to boot. Once I replaced the battery it would boot instantly when plugged in, even if we had run the battery down to where the machine shut off.

• The tech expected to find kernel panics in the analytics and said that these would indicate it was a hardware problem, not battery. He was surprised to not find them, but then changed his argument to the charging cable one. Do kernel panic logs always show up after a kernel panic? If an iPad shuts down spontaneously without leaving a kernel panic log, why is that happening? Any reason besides dead battery?

• This iPad seems to draw a lot of current. Back when it worked, if battery was half full and iPad was being used while plugged into a 1.5A (7.5W) charger we would generally see the battery level go down, not up. This would be unheard of on an iPhone, where using it while charging is the norm. As I see it, what's happening now is that it's drawing all the current its power circuitry allows for a device of this era (2015 before "fast charging") and is supplementing this with battery. But since the battery has failed, it can only do this for a minute or two and that's why it shuts down. Getting a new battery would allow it to run for many hours while plugged in or not plugged in.

• How many amps can this iPad actually draw while plugged in? How many amps can it draw from battery?

• The fair way to resolve this would be to actually replace the battery. If that fixes it, I pay $99. If it doesn't, I pay $599. But Apple is unwilling to actually replace the battery of this iPad and instead only offers replacement. This is unfair since it prevents us from establishing the truth that the battery was the problem.

• Since going to the Apple store when plugged into a 3.6A (18W) charger it now begins booting to the Apple logo and then shuts down after 30 seconds. It never gets to a normal screen. I would argue that the battery is holding even less of a charge so it's not supplementing the charger power as long as it was before.

Anyone have other thoughts or ways to frame my position to help me get treated fairly here?

Thanks.

I hate to say it, but it's probably not the battery.

However, he ultimately declared this to be a hardware problem, not a battery problem because he said he looked in some document that said that this iPad model would draw its power directly from the charging wire, rather than the wire charging the battery and the iPad drawing from the battery. Thus, if it's plugged in and still won't stay running, the battery is not the problem.

This is probably true. If you want to prove it one way or the other, you'll need to find an even higher-current charger. Any USB-C Apple charger with a USB-C to Lightning cable should work. A 96W MacBook Pro charger will certainly lay the question to rest. (This is fine.) If it runs on that, it's the battery. But if it doesn't, then it's not the battery.