If your Galaxy S24 or Galaxy S25 started running hot and draining fast after installing the One UI 8.5 update, you are not alone. Community polls show the majority of S24 and S25 owners report exactly this: phones that used to end the day with 30% battery now die by mid afternoon, and the device feels warm even while sitting idle.
The usual advice does not help, because this is not ordinary battery wear. It is a software problem with a few very specific causes, including a notorious Samsung Keyboard bug, and the fixes are different from what works on an aging phone. This guide covers the One UI 8.5 specific culprits and gives you 10 fixes in the order to try them.
Quick Answer
The biggest known culprit is Samsung Keyboard version 5.9.30.81, which can run in the background and drain battery even when you are not typing. Open the Galaxy Store, tap Menu, then Updates, and update Samsung Keyboard to the patched version. Next, go to Settings, then Battery, then Background usage limits, and put idle apps into Deep sleeping apps. These two steps resolve it for most users; the full guide below covers the 5G modem behavior and the remaining fixes.
Fix 1: Update Samsung Keyboard Past Version 5.9.30.81
This is the single most important fix in this guide. The version of Samsung Keyboard that shipped with the early One UI 8.5 builds, specifically v5.9.30.81, contains a bug that keeps the keyboard process active in the background long after you stop typing, consuming CPU and battery and even keeping the phone warm with the screen off. Samsung patched this in a newer build, so updating replaces the faulty process with the fixed one.
Exact steps:
- Open the Galaxy Store app (not the Play Store, because Samsung’s own apps update through Galaxy Store).
- Tap the Menu icon (three lines, bottom right), then Updates.
- Look for Samsung Keyboard in the list and tap Update.
- Restart the phone once so the old keyboard process is fully cleared from memory.
After 24 hours, go to Settings, then Battery, then Battery usage, and confirm Samsung Keyboard is no longer near the top with unexplained background activity.
Fix 2: Lock Down Background Apps With Background Usage Limits
One UI 8.5 changed how some apps behave after the update, and many apps that previously slept properly are now waking the phone constantly. Samsung’s built-in tool for this is excellent if you actually configure it.
Why it works: Every time a background app wakes your phone, the CPU spins up and the battery pays for it. Deep sleeping apps are fully frozen until you open them, so they cannot cause wakeups at all.
Exact steps:
- Go to Settings, then Battery, then Background usage limits.
- Tap Deep sleeping apps and add every app you do not need notifications from: games, shopping apps, streaming apps you rarely open, and social apps you check manually.
- Tap Sleeping apps and add apps you use occasionally but do not need instant alerts from.
- Turn on Put unused apps to sleep and set it to its most aggressive option.
What to check: Give this 48 hours, then compare the Battery usage screen. Deep slept apps should drop to near zero background time. If you miss notifications from one, move it back out.
If your drain started right after a software update, our guide to battery drain that starts right after an update covers the general post update behavior on every Android brand, not just Samsung.
Fix 3: Tame 5G and Modem Behavior on Weak Signals
Multiple users report that their S24 and S25 phones run noticeably warmer on One UI 8.5 when the signal is weak, and battery life collapses. The modem firmware bundled with the update appears more aggressive about hunting for 5G, which means the radio works harder and stays awake longer, generating real heat.
Why it works: On a weak 5G signal the phone burns as much power on the radio as the screen uses. Preferring a stable 4G connection stops the constant searching.
Exact steps:
- Go to Settings, then Connections, then Mobile networks, then Network mode.
- If you are in a weak signal area, switch from 5G/LTE/3G/2G (auto connect) to LTE/3G/2G (auto connect).
- Also turn off Wi-Fi scanning and Bluetooth scanning under Settings, then Location, then Location services, since these keep the radio hardware active even with Wi-Fi and Bluetooth toggled off.
Fix 4: Clear the Samsung Keyboard Cache and Wipe the System Cache Partition
Even after updating the keyboard, corrupted cached data from the buggy version can keep misbehaving, and the One UI 8.5 update itself can leave stale system cache that makes the whole phone work harder. Clearing the app cache removes the leftover data the buggy version wrote, while wiping the cache partition clears temporary system files without touching your photos, apps, or accounts.
Exact steps:
- Go to Settings, then Apps, then search Samsung Keyboard, then Storage, then Clear cache. Do not tap Clear data, or you will lose keyboard settings and learned words.
- Power the phone off, then hold Volume Up + Power until the Samsung logo appears.
- In the recovery menu, use the volume buttons to highlight Wipe cache partition, press Power to select, confirm, then select Reboot system now.
What to check: The first boot after wiping the cache partition takes a little longer, that is normal. If the phone felt warm at idle before and cool after, stale cache was contributing.
For Galaxy S25 owners, our Galaxy S25 battery draining fast fixes pair well with this guide for model specific settings.
Fix 5: Switch the Performance Profile to Light in Device Care
One UI 8.5 runs the CPU and GPU more aggressively than before on some S24 and S25 units. The Light performance profile dials this back with almost no noticeable difference in everyday speed, because less aggressive clock speeds mean less heat and less battery burn during routine tasks.
Exact steps:
- Go to Settings, then Device care, then tap Performance profile.
- Switch from Standard to Light.
- While you are in Device care, tap Memory and close RAM hogs, then Optimize now on the main Device care screen.
What to check: Use the phone normally for a day. If heavy games still run fine but the phone no longer gets warm during chatting or browsing, Light mode was the right call.
Fix 6: Hunt Down the Specific App Draining Your Battery
Sometimes the update did not break the system, it just changed background behavior for one third party app, which then went rogue. One badly behaving app can account for 20 to 30 percent of total drain, and the battery usage screen will name it.
Exact steps:
- Go to Settings, then Battery, then Battery usage.
- Look for any app with high background time that you barely used. Tap it and select Restricted so it cannot run in the background at all.
- If the worst offender is an app updated around the same time as One UI 8.5, uninstall it, reinstall the latest version from the Play Store, then re check after a day.
What to check: A healthy battery usage screen shows the screen and your most used apps at the top. Anything you did not open sitting in the top five with hours of background time is your culprit.
Fix 7: Turn Off Always On Display and Calm the Screen Settings
The screen is always the biggest battery consumer, and One UI 8.5’s new lock screen features can keep the display and its sensors more active than before. Always On Display keeps pixels lit around the clock, which is pure waste on a phone already fighting update related drain.
Exact steps:
- Go to Settings, then Lock screen and AOD, and turn off Always On Display, or at minimum change it from Always to Tap to show.
- Go to Settings, then Display, then Screen refresh rate, and make sure it is on Adaptive rather than forced to the maximum. Adaptive drops to low refresh rates when you are reading static content.
- Turn off Extra brightness and keep Screen timeout at 30 seconds.
Fix 8: Install the Latest One UI 8.5 Hotfix Build
Samsung typically follows a big update with small hotfix builds that address exactly these kinds of regressions. The build you got on day one may already be outdated.
Why it works: Hotfixes can include corrected modem firmware, fixed background scheduling, and the patched Samsung Keyboard bundled in, which attacks several causes at once.
Exact steps:
- Go to Settings, then Software update, then Download and install.
- Install anything available, even a small security patch, because hotfix notes do not always mention battery behavior.
- After updating, check the Samsung Keyboard version again in the Galaxy Store to make sure it is past 5.9.30.81.
Fix 9: Reset Network Settings to Fix Post Update Radio Bugs
Major updates can corrupt saved network configurations, leaving the Wi-Fi, Bluetooth, and mobile data stacks constantly retrying connections and generating heat. Resetting network settings wipes these corrupted configurations and forces the phone to rebuild clean connections, without touching your apps or photos.
Exact steps:
- Go to Settings, then General management, then Reset, then Reset mobile network settings and confirm.
- On the same screen, also run Reset Wi-Fi and Bluetooth settings, then reconnect to your Wi-Fi networks afterward, you will need to re enter passwords.
Fix 10: Back Up and Factory Reset (Last Resort)
If you have tried everything above and the phone still drains and overheats, something in the update migration is deeply broken on your device, and a clean reset is the only reliable fix.
Why it works: A factory reset removes every trace of the old system state, corrupted caches, misbehaving app data, and broken update leftovers, giving One UI 8.5 a completely clean start.
Exact steps:
- Back up everything first: go to Settings, then Accounts and backup, then Samsung Cloud, and back up, plus back up photos to Google Photos.
- Go to Settings, then General management, then Reset, then Factory data reset, and confirm.
- Set the phone up fresh rather than restoring every app at once. Install essentials first, use it for a day, then add the rest gradually so you can spot a rogue app if the drain returns.
Symptom vs Cause vs Fix at a Glance
| What you notice | Most likely One UI 8.5 cause | Fix to try first |
|---|---|---|
| Phone warm while idle, battery drops overnight | Samsung Keyboard v5.9.30.81 background bug | Fix 1: update the keyboard via Galaxy Store |
| Battery dies by afternoon with normal use | Apps not sleeping after the update | Fix 2: background usage limits |
| Phone hot outdoors or on mobile data | Aggressive 5G modem hunting on weak signal | Fix 3: switch network mode to LTE |
| Heat started right after installing the update | Stale system cache from the update | Fix 4: wipe cache partition |
| Warm during light tasks like chatting | Aggressive CPU clocks in Standard profile | Fix 5: Light performance profile |
| One app shows huge background hours | Rogue third party app after update | Fix 6: restrict or reinstall the app |
| Screen on time looks too high | Always On Display and refresh rate settings | Fix 7: screen and AOD settings |
| Everything got worse on update day one | Early buggy build of One UI 8.5 | Fix 8: install the hotfix build |
| Heat when switching Wi-Fi and mobile data | Corrupted network configuration | Fix 9: reset network settings |
| Nothing above helped | Broken update migration on your device | Fix 10: factory reset |
Frequently Asked Questions
Is the One UI 8.5 battery drain a hardware problem with my Galaxy S24 or S25?
No. The timing, right after the update, plus the Samsung Keyboard v5.9.30.81 bug and the modem behavior changes, all point to software. If the battery was healthy before the update, the hardware is fine.
How do I check my Samsung Keyboard version?
Open the Galaxy Store, tap Menu, then Updates, and find Samsung Keyboard. If it reads 5.9.30.81 with no update offered, check again in a day or two, since Samsung rolls the patched version out in waves by region.
Will putting apps in deep sleep break my notifications?
Only for the apps you choose. Deep slept apps cannot wake the phone, so you will not get their notifications until you open them. Keep messaging, email, and banking apps out, and only deep sleep apps whose notifications you do not care about.
Why does my phone overheat more on mobile data than on Wi-Fi after One UI 8.5?
Because of the modem behavior in Fix 3. On a weak signal the radio works much harder hunting for 5G, generating heat and burning battery. Wi-Fi uses far less power. Switching to LTE only on weak signals is the practical fix.
Is it safe to wipe the cache partition?
Yes. It only deletes temporary system files, while photos, apps, accounts, and settings are untouched. It is one of the safest troubleshooting steps on a Samsung phone.
Should I wait for Samsung to fix this instead of troubleshooting myself?
The hotfix builds in Fix 8 are Samsung’s official fixes, and you should install them. But the keyboard update, background limits, and network mode changes in this guide are things no future update configures for you, and they improve battery life on any One UI version, so do them regardless.
The Bottom Line
The One UI 8.5 battery drain and overheating problem breaks down into a handful of fixable software issues. Start with the Samsung Keyboard update in the Galaxy Store, since that single buggy version explains the worst cases. Then lock down background apps and calm the 5G modem, and most Galaxy S24 and S25 phones return to all day battery life. Work through the remaining fixes only if you need them, and keep installing Samsung’s hotfix builds as they land.
