My (android) phone is losing 20% battery overnight. How can I track what is causing this? The built-in battery usage chart doesn't have any useful info. Any app that I can use to track battery usage?

Long back a app called better battery stats used to give detailed insights. Not sure if it still works on recent androids.

I'd recommend better battery stats as well. It's been taken off the Play Store. You can get builds at https://forum.xda-developers.com/t/app-2-2-05-oct-v2-4-betterbatterystats.1179809/

I am gonna use this app as well to test it As far as i noticed, in my bedroom there is network fluctuations so i think that is major battery draining thing,I kept in flight mode and one day it was not much reduced.

Looks like i’m very lucky, my xiaomi device is very robust in terms of battery such that even if it’s 3% while i go to bed, i can be sure that i get to hear alarm ring and not drop a single %

Alarm can ring even when phone is switched off 😉

It's time to replace the old battery.

No. No music. Battery health also looks fine. It works fine throughout the day. Only drains overnight.

sleep tracking..😅