Outside of the case? You'll lose power in a few days. If you keep them in a location where they aren’t near an Apple device where they could go into fast pairing mode or whatever, they might hold a charge longer, but outside of the case and within a few feet of your Apple devices, they’ll lose power unused in a few days.
Even in the case, you're still going to have a hard time reliably using these if you don’t touch them very often, unless you make a point to charge them. No matter what anyone tries to tell you, low-power mode is not a replacement for having an actual power button.
The good news is that they do charge pretty fast, to at least get you over that dead to juice hump.
But this is one of my biggest complaints against AirPods Max: not only is overall battery life pretty poor compared to the other headphones in its price range (Sony, Bose, Sonos), but they don’t hold a charge when not in use unless you always put them back into the stupid bra.