Why your phone battery drains overnight (and how to stop it)
My phone used to drop from 90% to 50% overnight just sitting on the nightstand. Took me about a week of poking around to actually figure out why. Here's the order I'd check things in if I were starting over.
First thing I'd say: don't start turning settings off randomly like I did at first. That wasted a few days and didn't help, because I was guessing instead of actually checking what was using the battery.
Start with the battery usage screen
On iPhone it's Settings → Battery, scroll down to the last 24 hours. Android is Settings → Battery → Battery usage. In my case it was Facebook sitting at 28% overnight, even though I hadn't opened the app since the afternoon. If one app is way higher than the rest while you weren't even using your phone, that's where to start.
Background refresh is usually the actual cause
Apps you're not using are still allowed to "wake up" and check for new content in the background that's what was happening with my Facebook. Turning it off app by app worked better for me than the blanket toggle, since I still wanted messaging apps getting notifications instantly.
- iPhone:
Settings → General → Background App Refresh - Android:
Settings → Apps → [app name] → Battery → Background usage
If it's not an app, check location
A friend of mine had this exact issue with a navigation app that had a bug it kept polling GPS even after he'd force-closed it. You won't see this unless you specifically check, since the app icon isn't even open. Worth a look if step one didn't show an obvious culprit.
Always-on display adds up more than you'd think
I like always-on display during the day, but it's pointless at night since I'm asleep. Switching it off between midnight and 7am made a noticeable difference for me small thing, but it stacks with everything else.
Weak signal overnight
If you live somewhere with bad reception basement, far corner of the house, whatever your phone keeps working harder to hold a signal, and that costs battery. If you don't need calls while sleeping, Airplane Mode with Wi-Fi turned back on fixes this completely.
Last resort: actual battery health
If you've gone through all of the above and it's still draining fast, check Settings → Battery → Battery Health. Mine was at 84% last I checked, which is fine, but anything under 80% starts behaving oddly, including faster idle drain. At that point it's a battery swap, not a new phone.
Honestly, just start with step one
Of everyone I've talked to about this, almost all of them had it solved by checking which single app was the problem and turning off its background refresh. Don't overthink it check, don't guess.
One extra check I would make
One thing I would not do is install a “battery saver” app from a random store listing. Most of them add another background process, which is the last thing you need when you are already chasing idle drain.
Quick answers
Why does my phone battery drain overnight when I am not using it?
Usually one app is waking up in the background, location services are running, signal is weak, or always-on display is active. The battery screen is the fastest way to find the real cause instead of guessing.
Is overnight battery drain normal?
A small drop is normal, but losing 20% or more while the phone sits idle usually means something is running in the background or the battery health is getting weak.
Should I replace my phone battery for this problem?
Only consider a battery replacement after checking app usage, background refresh, location, signal strength, and battery health. If battery health is below about 80%, replacement may be the real fix.