Guys, I had the same Issue.
I got them a week ago, in the release day, and they were working perfectly. At least until Friday. That I charged them fully, and by Saturday night, they were dead again, and I barely used them, which I found weird.
I noticed that over nigh (Saturday night and Sunday night) they were draining around 40-50% (depending how many hours I sleep haha) of battery. And they were inside its smart case the whole time.
Yesterday (Monday) started doing my test: at 8am I unplugged them, they were at 100% battery. I kept them in their smart case. At 10am they were 92% of battery. At 11:37am they were 87%. All without using them, and inside the smart case.
SOLUTION
I factory reseted by pressing the crown and the noise control button at the same time for 15 sec, till the flash light blinked amber and then turned white. Then connected to my iPhone again.
Today I did my test again: I unplugged them at 8am, they were 100% battery. and I kept them in the case. 4 hours later at 12pm, they were still 100%. 4 hours later at 4pm, they were still at 100% battery. Now, at the moment im writing this, 2:30 later, at 6:30pm, they are at 100% of battery.
So I conclude that this solver the problem, because after more than 10 hours in its case, the battery remained intact.
CAUSE
So far I think the issue is that its processor got stuck and never stopped working, even though they were inside the case, because the rate batterydrain/hour was almost the same as when playing music (average 4%).
But we got to find out what is causing tis processor to get stock. Maybe we find a patter in our behavior using the headphone.
So far, I did play music from all my devices (iPhone 12 Pro, iPad Pro, MacBook Pro, Apple Watch, Apple TV HD, Apple TV 4K) when I was trying my headphones. I was especially trying the switching among devices feature, so I was constantly trying the automatic switching.
I read in this threat that a lot of you were also playing among several devices. So my theory is that the switching feature or the streaming from certain device is causing its processor to get stuck.
I also read that they just release an update for the AirPods max firmware yesterday ( 3C16 ), so it my have coincided with the solution as well.
Please let me know your comments.