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.