Convergence: battery is constantly discharging/charging
#1
Hi folks,

Today I share an interesting find with the PinePhone's battery profile when using it with the convergence dock. 
I've installed Cronie and shell script which sends the battery voltage and level (percentage) to my RPi server every minute. (from /sys/class/power-supply/axp20x-battery/)
The server then is able to plot a graph of these measurements.

When fully charged (at 86%, due to the 4.2v safety limit being applied) and plugged in with convergence dock (USB-c charger, HDMI display, usb keyboard/mouse, media playing so it won't go to sleep), the graph reveals that the battery does not stay at the same level but constantly discharges and then recharges again.

   

With a laptop for example, this does not happen. It stays at 100% and the voltage is constant.

How does this affect the battery in terms of longevity and efficiency?
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#2
This is rather interesting, thank you for sharing!  Could you, please, provide the output of the following command as well, in the scenario you've decribed in your post, i.e. with the official dock connected to the phone, the same USB Type-C charger connected to the dock, etc.:

Code:
cat /sys/class/power_supply/axp20x-usb/uevent

Did you experience any flickering of the phone's screen backlight while running those tests?

Could you also, please, re-run the data acquisition and plotting of the charts with the same USB Type-C charger connected directly to the phone, i.e. without using the official dock?  Please, provide the second output of the command above as well.
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#3
I'm pretty sure this is intentional. I seem to remember reading that cyclical charging/discharging is a feature of the operating system to increase battery life.

The only reason I recall that is that I recall thinking how much I hated the phone I had that did this, when I read about the Pinephone doing it. There's nothing more irritating than charging your phone overnight and having it at 50% when you need it in the morning.
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#4
Please, have a look at this forum post, in which I've described in detail the background of why the PinePhone battery doesn't charge to 100% in the default configuration, how to change that if desired, and why changing that isn't the best idea at the moment.  As a note, the original question in this thread is about the phone battery constantly discharging a little and charging back, despite the charger being connected all the time.
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#5
The reason that the phone discharges slowly, even though a charger is connected is because the modem and the WiFi chip is connected directly to the battery. The two items can therefore never be powered directly from USB charger.
For same reason, if you have discharged your battery to 0% (<=3.0V), and you power up the phone from USB, you will most like see, that WiFi and Modem is not working on the phone. Battery has to be charged to over 3.5V, before they will work again.

This has btw nothing to do with the dock - the phone does the same with power connected directly to the USB port.
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#6
That's correct, Alho.  Thank you for pointing it out!  As a note, following the "4G-VBAT", "VBAT_BB" and "VCC-WIFI" labels in the PinePhone schematic clearly shows where the modem and the WiFi/BT module get their power from.
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