I tried to gather some quantitative measurements on power-use. This is with
- Fedora Core 35 with TLP installed, running default Gnome/Wayland as desktop
- 11th Gen Intel(R) Core™ i7-1165G7 @ 2.80GHz
- 16 GB of main memory installed
- Bluetooth and WiFi on (Wifi connected; Bluetooth not actually being used)
- kernel 5.15.18-200.fc35.x86_64 (awaiting clean-up of the 5.16 regressions)
I’ve measured charge drain by looking at /sys/class/power_supply/BAT1/charge_now. As far as I can tell, this reports in µAh, and it looks like the system normally converts this to Wh by multiplying with the value in /sys/class/power_supply/BAT1/voltage_min_design which seems to report 15.4V (in µV). So as far as I can tell the charge in µAh can be converted to Wh by multiplying by 1.54e-5
I’ve sampled the charge in 1 minute intervals, storing a time stamp with it, and then computed the average power drain over relevant periods by dividing by the time elapsed (when the system is suspended, obviously no measurements are recorded, but the time stamps tell you when the measurements were taken)
Measurements were mainly made when the battery was in the 40%-80% charge range.
I was mainly interested in determining the idle power drain, so I’ve mainly used measurements over periods where I was not using the computer.
System on, locked and screen off, with HDMI & USB expansion cards: around 3W
s2idle sleep with USB-A and HDMI expansion cards: around 1.9 W
s2idle sleep with only USB-C expansion cards: around 0.8 W
deep sleep with USB-A and HDMI expansion cards: around 0.9 W
deep sleep with only USB-C expansion cards: around 0.4 W
Conclusions:
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The normal idle power drain on the system is pretty good! Even with the screen on and no/very little work happening (reading a PDF document?) I’ve seen power drains around the 4W range (with low screen brightness). It doesn’t seem to matter very much if the HDMI and USB-A cards are inserted.
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s2idle is really quite disappointing: it doesn’t even double the time the battery will last compared to just leaving the machine on! Removing the USB-A and HDMI cards improves the situation a little bit.
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deep sleep is very badly impacted by USB-A and HDMI cards. I don’t know if the base line 0.4W is as expected to keep 16Gb of memory functioning. With a 55W battery, it certainly does give a respectable suspend time.
It may well be that my methodology can be improved, but it feels to me these are figures that reflect how I’d consider “not using” the machine (for use, obviously I’d expect more power use, but then I’m getting something for it).
I really hope something can be done (in linux? in the BIOS?) to reduce the penalty of having a USB-A and HDMI card present. Presently, the locking system on the cards is so tight that unplugging them is really quite uncomfortable. I did install one on each side, because I want to have a USB-C on either side, for choosing charging position.
I bought the USB-A and HDMI mainly for travel, when battery life actually is important.
In the measurements above I did not include hibernation, because FC35 does not enable that by default, so if I can get acceptable results without it, I’d rather not go through the hassle of enabling it.