Overnight, starting from a 100% charge, all apps closed, even from a fresh reboot, screen of course off, my phone (Redmi 6) ends up with a ~90% charge. I know this is abnormal, as my previous phone (Redmi 5A, with worn out battery) ends up with ~99% in the same situation.
That's quite annoying to know that something needlessly drains my battery! I'm pretty sure it's due to some software bug. Encountering the issue as well on MIUI 10 and 11.
I'd like to find out the culprit in order to fix the issue. What can I do?
For the record, my syslog receives the following two errors a lot (several per second):
BoostFramework() : Exception_1 = java.lang.ClassNotFoundException: com.qualcomm.qti.Performance BoostFramework() Ux Perf : Exception = java.lang.ClassNotFoundException: com.qualcomm.qti.UxPerformance
(then, just in case, I went to the Developer options and fully disabled logging, who knows! But it didn't fix the battery issue.)
Also for the record, I have already done a lot of googling about that battery drain issue, and tried the following fix: Go to "Settings > App > Permissions > Autostart" and disable everything (in my case I only had "Camera" enabled). Sadly, it didn't fix the issue.
I've had run "Battery usage stats" during the day, and it reported me that the screen was most (like 90~95%, as I recall) using the battery, followed by a few % by the networks (cell, wifi).
But here I just looked at "Battery usage stats" and it gave me interesting results: Screen 35%, Cell standby 31%, Wifi 24%…
This is something I was also suspecting. It's highly possible the battery drain is caused by network (both cell and wifi) activity, which in turn could be caused by some software bug. Even though I made sure that no apps or widgets are running. What could I do to investigate further this path? Maybe there is some setting (possibly advanced) that could fix the issue?
As suggested in the comments, I tried "airplane mode" (i.e. cell and wifi networks disabled) and it seems to solve the issue. I think that both, cell and wifi, cause battery drain.
However, that adds an annoying handling step, and I cannot receive calls while in airplane mode. I wish I could avoid that extra handling. I usually don't use wifi, so I'll try disabling only wifi and see if it's sufficient.
The MediaTek chipset of the Redmi 6 definitely seems to be a bad pick. This chipset forbids almost any custom ROM, and now I discover it's not energy-efficient at all for networks…
Some feedback after an extensive period of testing. I can keep cell network and mobile data always on, turning the wifi off seems to be sufficient. Overnight, the battery goes down to barely 99%, it reaches 98% at the very worst… sometimes it even stays at 100% :)
Coupled with a good mobile plan, I just keep the wifi always off, and no longer think about this issue :)