I can certainly understand how frustrating it must be to experience such significant battery drain, especially when your Beats 360 are advertised to provide over 30 hours of battery life. Losing around 15% battery overnight while powered off, along with getting only 4–5 hours of playback, is certainly concerning.
Without knowing what you have tried so far yourself, except you've already tried disabling Find My without improvement, I'd recommend trying the following:
- Reset your Beats 360: Press and hold the Power button and Listening Mode button together for approximately 10 seconds, until the status light flashes five times.
- Reconnect your headphones: Pair them with your device again after the reset.
- Check for firmware updates: Make sure your Beats are running the latest available firmware.
- Monitor battery performance: Fully charge the headphones, turn them off overnight, and check whether the battery continues to drain.
If the issue persists after these steps, I would recommend contacting Apple Support for further diagnostics and a possible warranty service evaluation. To do so, just click on the "Support" link on the bottom left-hand side of this forum's web page.