Couple things I could think of, that can lead to this sort of behavior:
- Using them in a cold environment, like -20 to -30 degrees Celsius.
- Headphones dropping down to an older standard for some reason, and connecting e.g. via bt 4.x or using an incorrect codec (would explain why one of them is draining so much faster) โ should be possible to check in BT settings
- The headphones just have a bad battery, I've run into multiple headphones which just turn off once the battery reaches 50-60 %, especially when it's cold out
But these are just suggestions and speculation, I'm not really an expert on the subject.