[Q] Battery level is incorrect only in bootloader?

[x3r0.13urn]

Hi,

Recently my Redmi Note 8T battery percentage acts weird, after I had it charged to 86%, it quickly dropped to around 50%, then it turned off itself, bootloop-ing countless times.
Strange enough if I have it plugged to any power source it would turn on, but as soon as I unplugged it, it turned off, sometimes immediately, sometime after usage of 2-5 minutes.

My phone is unlocked, and for years I never use root except to restore data. Only custom roms + gapps. And my storage is not encrypted (use dfe).

I know it's battery problem, but my main question is: I'm able to enter twrp or ofox, and it shows battery percentage.
And while in recovery, it never turn off itself, it's like the battery is working properly, I'm able to use it for long time, tried 1-2 hours before I hit power off from recovery.
But as soon as I hit reboot to system without any charger plugged in, it's bootlooping again.

I tried to swap to different kernel, they didn't help. So I suspect the issue isn't coming from kernel.
Just somehow the battery percentage stored in bootloader (?) or something else and the percentage read by twrp/ofox is different

What I'm able to:
1. Boot the device with charger plugged in
2. Boot to any recovery
3. Boot to fastboot

What I haven't do yet:
1. Flash back original miui EEA
2. Format data
3. Let the battery empty and charge it after it

I'm not sure about format data would help, I just do clean flash every time change rom.
About flash to miui, I noticed sometime phone displays the original offline charging indicator (the big battery icon with color) shows empty when rebooting (just before going bootloop).
But when I offline charge (using custom roms) and got different display of offline charge (I believe the custom offline charge from the roms), the percentage shows the same as being shown in twrp/ofox.

Does anyone here knows maybe how to reset/recalibrate battery level in the bootloader (?, again I'm sorry, I'm not sure where it's located) so it can show correct data as same as what being read in recovery?

 

[SkyFlex]

That's sign of your battery is dying. There is plenty of thread about it in this forum also with different phones.

Just replace the battery, or you can bypass the fuse(?) on the bms if you don't want to replace the battery, idk how safe it is though.
You already know it, its not software issue, you cannot recalibrate, there is no way around it

I just facing same issue for the past few days, I tried everything i can from software side, nothing works. In the end, I just replace my battery and now everything working just fine.

 

[x3r0.13urn]

That's sign of your battery is dying. There is plenty of thread about it in this forum also with different phones.

Just replace the battery, or you can bypass the fuse(?) on the bms if you don't want to replace the battery, idk how safe it is though.
You already know it, its not software issue, you cannot recalibrate, there is no way around it

I just facing same issue for the past few days, I tried everything i can from software side, nothing works. In the end, I just replace my battery and now everything working just fine.

Yes, I was wondering if there's anyway to fix it without going to service centre or DIY opening its backcover and change the battery, lol.

I never heard of bms, what is it?

As for now, I have left it more than 24 hours on ofox and the battery is not drained yet, so obviously, the battery itself still has some juiced in it yet cannot be used outside recovery/fastboot mode.

 

[SkyFlex]

Yes, I was wondering if there's anyway to fix it without going to service centre or DIY opening its backcover and change the battery, lol.

I never heard of bms, what is it?

As for now, I have left it more than 24 hours on ofox and the battery is not drained yet, so obviously, the battery itself still has some juiced in it yet cannot be used outside recovery/fastboot mode.

Its Battery Management System. A little board mounted on the battery.
What bms does? The name is self-explanatory, that little board have responsibility for protection, monitoring like thermal, battery health, regulate charging and discharging, something like that.

Probably because in recovery/download mode it didn't draw much power from the battery compare to booting up device or doing heavy task. So the bms like "Alright, that's safe enough".

If you want to try to "recalibrate", try deleting batterystats.bin under /data/system, also under battery-history and battery-saver folder

 

[x3r0.13urn]

Its Battery Management System. A little board mounted on the battery.
What bms does? The name is self-explanatory, that little board have responsibility for protection, monitoring like thermal, battery health, regulate charging and discharging, something like that.

Probably because in recovery/download mode it didn't draw much power from the battery compare to booting up device or doing heavy task. So the bms like "Alright, that's safe enough".

If you want to try to "recalibrate", try deleting batterystats.bin under /data/system, also under battery-history and battery-saver folder

Nah that "calibrate" process was a placebo, it was known for it long ago. Anyway, your hunch is correct. The battery's fuse was blown. Had to replace the battery, don't want to mess with solder.

I was quite surprised as my daily usage never been heavy and I'm quite careful using it. I never play any games on the phone. Never use it when it's being charged. Rarely overcharged it. Charge always around 20-30% to 85-92%. Use original charger, just recently I switched to Xiaomi 33w. Yet still the fuse was blown after all. Not sure whether the 33w charger was the culprit.

 

[SkyFlex]

Nah that "calibrate" process was a placebo, it was known for it long ago. Anyway, your hunch is correct. The battery's fuse was blown. Had to replace the battery, don't want to mess with solder.

I was quite surprised as my daily usage never been heavy and I'm quite careful using it. I never play any games on the phone. Never use it when it's being charged. Rarely overcharged it. Charge always around 20-30% to 85-92%. Use original charger, just recently I switched to Xiaomi 33w. Yet still the fuse was blown after all. Not sure whether the 33w charger was the culprit.

Same case here, I used 18w charger ( Aukey PA-T9 ) never charge below 20-30% since I bought this device, I'm pretty sure my battery wear still quite good, the battery also physically good not swollen, just the fuse. Although for the last few months I've been using the phone while charging ( watching live stream on Twitch ) which I know the app is used high cpu usage compare to youtube/local video player ( MX player )

Probably not, but who knows, I don't want to dig deeper what cause it, I'm not knowledgeable about electrical, but I do think the fuse worn off for some reasons and blow under normal loads.
For me its been around 3 years, the battery need to replace anyway.