reported charge drops even when power stays steady

[Selene ToyKeeper]

On Ubuntu Touch devices, I've noticed that the battery indicator and graph continuously decrease while the device is unplugged, even if the phone's power supply stays rock steady. This can lead the phone to report critical battery status when the battery is full.

I ran an overnight test on an arale, in which I set the phone's power supply to 4.20V with the screen always on but dimmed as far as it will go. The battery is a 4.35V cell, so its useful range should be about ~3.30V to 4.35V, with 4.20V being a high but not full charge. Ideally, the battery indicator should show a high charge like 80% or so, and keep displaying that as long as the voltage doesn't change. Instead, the display went from 100% to 1% over a period of about 14 hours. At 10%, 5%, and 2%, it popped up low/critical battery warning dialogs (despite the power source still being at 4.20V).

The resulting charge graph is attached below. Ignore the part where it says 67%; I accidentally caused the phone to reboot before I could get a screenshot, so the power indicator in the screenshot is after it had a chance to reset its value.

BTW, the kernel has correct data on the voltage in /sys/class/power_supply/battery/voltage_now so the error is probably somewhere up in a higher layer.

Version info:
> adb shell cat /etc/system-image/channel.ini
[service]
base: system-image.ubuntu.com
http_port: 80
https_port: 443
channel: ubuntu-touch/rc-proposed/meizu.en
device: arale
build_number: 62
version_detail: ubuntu=20150717,device=20150709-8965e37,custom=20150709-814-6-40,version=62

I recall seeing similar behavior on krillin, but have not explicitly measured it.

[Pat McGowan (pat-mcgowan)]

I am unclear if this is reflecting something users will see

[Selene ToyKeeper (toykeeper)]

This ties in with bug 1471913, in which people are getting all sorts of weird and false reports about the battery charge. Fixing that bug would likely fix this one too, though they're not strictly the same bug.