I have an external 21700 battery bank which provides usb-power for my laptop. It provides enough watts for my laptop to charge its onboard batteries while providing the running power. This is rather silly: if I'm using the external battery then I intend to deplete it fully, so it seems inefficient to charge an onboard battery depleting the external one faster just to then deplete the onboard battery. This battery-charging-battery costs energy and charge cycles of both units.

Is there a way to tell my computer NOT to pull voltage to charge the system, but just to use that for running power?

Note: I'm using a 8th gen X1 Carbon (relatively new) with 10th gen Intel tech.


For this model, you want acpi_call, then use the option to define charge thresholds.

Basically the idea would be to set the maximum percentage to which the battery should be charged to the current charging level once you plug in the external power bank, e.g. 43%

 cat 43 > /sys/class/power_supply/BAT0/charge_stop_threshold

Calculate the current battery level with the values in these two files:


Then it is a matter of activating and the threshold and removing it with a little script triggered by the plug-in/-out events. This udev-rule would do.


The Lenovo battery gadget used to have a manual setting for battery charging, like start charging only when battery charge has dropped below to X%, and then stop charging once battery charge has reached Y%. This is extremely useful. When I plug in a charger at a time when my battery is between X and Y, then it doesn't automatically start charging anything -- it just uses whatever juice it needs for only running the laptop. Extremely useful, because it avoids those constant and useless charging cycles that only shorten the battery life. If I've set those settings to, say, 35% and 85%, and my laptop is at 60% when I plug in the charger, then it will just stay at 60% the whole time. Also useful when I plug into my car, and the engine is not running: I wouldn't want to unnecessarily deplete my car batttery -- just use the tiny little bit of juice that is needed to run the laptop. To this day I am using this gadget, and I am afraid to upgrade it, because its newer versions no longer have that setting.

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