Why does Android lose 15-20% battery overnight in Airplane Mode?

I'm trying to figure out why my Android phone loses around 15-20% battery overnight, even when it's in Airplane Mode with Wi-Fi, Bluetooth, and mobile data turned off. Here are a few things I've already tried: reduced screen brightness. Disabled background apps. Turned off location services. Updated the phone to the latest available software. Battery health still appears to be normal. I'm not sure if this is caused by a particular app running in the background, the battery starting to wear out, or a system setting that I'm missing. What would you recommend checking first? Are there any reliable methods to identify what's consuming power while the phone is idle?

techycorner247 wrote:

What would you recommend checking first?

Start with the simplest steps possible.
Check the battery’s charge level.

>>21945534 Hello,

techycorner247 wrote:

Are there any reliable ways of finding out what’s using power when the phone is in standby mode?

Well, you know — a reliable answer would probably come from a specialist service that really gets to grips with the issue, but that’s not the sort of answer you’re looking for.

Start with the tools you have on your phone: Settings --> Battery --> Battery usage since last charge.
In other words — charge your phone in the evening, ideally using a USB meter (when it shows 0W charging = fully charged), leave it overnight, and in the morning check the logs — which apps and system processes were running. Analysing these logs should already give you a clue.

There are also apps for this, e.g. DevCheck — it shows processor activity as well as current battery consumption. I checked my own phone — it showed 21 mA of current consumption, with Wi-Fi, the phone app and the screen on, whereas on yours nothing is running, yet you’re seeing around 150 mA or more. It’s worth checking.
Another app is GSam Battery Monitor, which will show whether the phone enters sleep or deep sleep modes and for how long. It looks as though yours isn’t entering these modes at all, but… what if it is, and a dead battery is to blame?
You see, this is the sort of information you can analyse and draw conclusions from.