Samsung S25 Ultra unexpectedly turned off at a 78% battery level. Refused to turn back on for over 18hrs. Eventually displayed 0% battery level and requested for a charger to be inserted, exactly 18hrs later. Samsung Service center couldn't confirm what the issue was, said perhaps Knox software probably updated during that time, that could have required the device to be off. Is this normal ?
Being locked out of my cellphone whilst traveling was a nightmare!
Hi You’re absolutely right to be concerned, that situation is not normal, especially for a flagship like the Galaxy S25 Ultra. Let’s break down what likely happened and what you can do to prevent it again.
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🔍 What Probably Happened
There are three main possible explanations for this:
1. System or Knox Security Update Glitch
Samsung’s Knox security layer can indeed perform background firmware or security updates that require a brief restart — but not an 18-hour blackout.
It’s possible that during a background update, the boot process froze due to a firmware or battery controller error, leaving the phone in a “sleep-dead” state (neither off nor booting).
2. Battery Management Controller Crash
Modern Samsung batteries have smart controllers that regulate voltage and temperature.
If the controller crashed (for example, due to a spike during charging or update), the system can misread battery data — showing 78% before shutdown and then 0% when it finally restarted.
This can also happen after thermal throttling or sudden voltage drops.
3. Deep Sleep/Boot Loop Prevented Wake
Some Galaxy devices on One UI 8 / Android 15 betas have experienced random system sleeps where the device won’t power on until it internally resets after a timeout (often between 12–24 hours).
This is rare but has been reported by some S25 Ultra and S24 users after security updates.
⚙️ What You Can Do
Here’s what I recommend step-by-step:
1. Update Everything
Go to Settings → Software update → Download and install.
Also check Settings → Security and privacy → Security updates (Knox patches sometimes come separately).
2. Perform a “Wipe Cache Partition”
Power off completely.
Hold Volume Up + Power until you see the Samsung logo.
Navigate with volume buttons → choose Wipe cache partition → Yes → Reboot. (This won’t erase your data — just clears system cache.)
3. Battery Calibration (Important)
Charge to 100% without interruption.
Let it drain naturally to 5–10%.
Charge back to 100% again.
This helps recalibrate the battery controller’s readings.
4. Monitor with Samsung Members App
Run “Diagnostics → Battery and Performance.”
Look for anomalies in battery temperature or “Abnormal app activity.”
5. Enable Auto Restart
Settings → Battery and device care → Auto optimization → Auto restart at set times (once a week helps keep firmware stable).
⚠️ If It Happens Again
Note the exact date and time, and whether the phone felt warm before it went off.
If it happens a second time, insist on a device log report at a Samsung Service Center — they can pull system logs (via Smart Switch or Knox logs) to see what process triggered the shutdown.
💬 In Summary
No, — an 18-hour unresponsive period at 78% battery isn’t normal, and the explanation about Knox “updating in the background” doesn’t fully account for it. It’s most likely a firmware-level battery or system controller hang, and a cache wipe + update should stop it from repeating
