There’s a magnetic contact that the “bra” case engages that turns off the headphones so the battery doesn’t needlessly drain. Bunch of companies make after market cases/covers, you should get one of them at least.
Also in my experience, the brassiere was never perfect about guaranteeing the AirPods Max were put perfectly into a sleep state. The same exact issue could sometimes occur, maybe an alignment issue. The AirPods Max sound fantastic, but there's a lot of little details about them where Apple just kind of dropped the ball.