https://wccftech.com/airpods-max-battery-drain-issue/

There are a growing number of AirPods Max owners complaining of the premium headphones losing their battery charge overnight. Even when the battery level is at 100 percent, it’s reported that the AirPods Max went from being fully charged to 1 percent and even 0 percent overnight. Remember that these drainage issues are happening even with the headphones placed inside Apple’s official case, which puts them in ultra-low power mode.

A Reddit thread started by u/Linkistinki discusses the same problem, and a lot of users are complaining of the same battery drainage issue.