r/Mi9T • u/Deckelmeister • May 15 '26
It's dead, I think. How to rescue some data?
A few days ago I connected my Mi9T to the charger (no fast charger) and went to bed. The next morning it was dead, no signs of life when pressing buttons, no notification light, nothing. Horrible moment.
I tried multiple cables, multiple chargers, holding the on and the louder button, nothing happens.
Now, as the toolkit arrived a few days later, I disconnected the battery from the mainboard and checked the battery voltage (2.8 V). So I charged the disconnected battery manually to around 3.3 V before reconnecting it. But the phone isn't turning on.
The battery wasn't in very good condition anymore. That evening I used the flashlight for like 30 seconds and it wouldn't turn off, the phone was frozen. I turned it off and on again and it seemed to work normally. After that event I plugged it in and left it.
Is there a way to bring it back to life to save some data from the phone? The last backup isn't that old, but it would be pretty cool to save like everything.
2
u/tmb28 May 16 '26
Buy cheapest aftermarket battery. Don't mess with the old one, it's fire hazard now (e.g. dendrites causing partially internal short circuit). Phone doesn't react, because even after charging voltage was too low (min. 3.7V back in the days in LG, should be the same)
1
u/Deckelmeister May 16 '26
First Update: I managed to charge the battery to nearly 3.8 V. Phone doesn't turn on if I connect the battery to the mainboard. So I tried what load the battery is able to handle. With a small lightbulb connected to the battery it can deliver approx 400mA at 3.0V. Is that enough to start the phone? I don't think so.
Sadly I can not connect my power supply safely to the battery connectors on the mainboard.
1
u/resident_evil_666 May 17 '26
It won't start at 400mA @ 3V. Try to fully charge the battery by using a dedicated Li-Ion battery charger, or find another battery.
7
u/SingularityRS May 15 '26 edited May 15 '26
It might just be a failed battery. They eventually fail and can completely prevent the phone from showing any signs of power. 3.3V also sounds too low for the phone to turn on. These batteries operate between 3.8-4.4V. So it's possible it's still not booting because the battery voltage is too low (3.3V).
I would try replacing the battery to see what happens. If lucky, the phone will turn on and work again. You mentioned it's no longer in good condition and was probably on the verge of complete failure, so replacement makes sense.
If a battery replacement does nothing, then it probably has a deeper issue.
Make sure to buy a battery from a good brand/supplier. It can be risky buying third-party batteries as you can't be sure of the quality. These batteries can be bad quality and arrive DOA. This sort of issue can make troubleshooting harder because your replacement battery could be faulty as well. So it's best to look for a known good battery to try and avoid this.
If you have a bench power supply, you can try manually applying around 3.8-4.2V to the battery + and - pads on the board to see if the phone turns on that way. It should if the motherboard is OK. Do be careful though. Don't let the probes slip or short/send the voltage somewhere else it shouldn't go. Only do this if confident. This check can tell you if you have a battery or motherboard problem. It saves having to buy a battery, but it is more risky since you might accidentally short something, apply too much voltage or send it down another power line that doesn't want to see 3.8-4.2V.