Hi rday, Your understanding of the start/end thresholds is correct — the battery *should* start charging at 75% and stop at 80%. If your Dell laptop keeps charging past 80%, it usually means the firmware/EC does *not* actually support Linux-controlled charge thresholds, even though the sysfs files exist. On many Dell models, the kernel exposes charge_control_*_threshold, but the hardware ignores them unless the feature is supported by the Dell WMI battery driver or configured directly in BIOS. A few quick checks: lsmod | grep dell modprobe dell-wmi-battery # if supported If dell-wmi-battery is missing (common), Linux cannot enforce thresholds. In that case, charging limits must be set in the BIOS (“Custom Charge”) if available — otherwise they cannot be controlled. In short: the sysfs interface is present, but your firmware isn’t honoring it. Best, Qingwei On Mon, 1 Dec 2025 at 11:43, Robert P. J. Day via linux < linux [ at ] linux-ottawa [ dot ] org> wrote: > > (i'm using debian 13 on a dell pro max 16 laptop, but i suspect this > question applies to any linux distro that supports battery charging > configuration.) > > read recently that i shouldn't keep my laptop plugged in and maxed > out at 100% charge perpetually since that allegedly reduces the life > of the battery. so i read that i can play with the settings for > battery charging under /sys/class/power_supply/BAT0: > > -rw-r--r-- 1 root root 4096 Dec 1 10:21 alarm > -r--r--r-- 1 root root 4096 Nov 27 04:29 capacity > -r--r--r-- 1 root root 4096 Dec 1 10:21 capacity_level > -rw-r--r-- 1 root root 4096 Dec 1 10:19 charge_control_end_threshold > -rw-r--r-- 1 root root 4096 Dec 1 10:19 charge_control_start_threshold > -r--r--r-- 1 root root 4096 Nov 27 04:29 charge_full > -r--r--r-- 1 root root 4096 Nov 27 04:29 charge_full_design > -r--r--r-- 1 root root 4096 Nov 27 04:29 charge_now > -rw-r--r-- 1 root root 4096 Dec 1 10:21 charge_types > -r--r--r-- 1 root root 4096 Nov 27 04:29 current_now > -r--r--r-- 1 root root 4096 Nov 27 04:29 cycle_count > lrwxrwxrwx 1 root root 0 Nov 27 04:29 device -> ../../../PNP0C0A:00 > -r--r--r-- 1 root root 4096 Dec 1 10:21 eppid > drwxr-xr-x 3 root root 0 Nov 27 04:29 hwmon0 > -r--r--r-- 1 root root 4096 Nov 27 04:29 manufacturer > -r--r--r-- 1 root root 4096 Nov 27 04:29 model_name > drwxr-xr-x 2 root root 0 Dec 1 10:21 power > -r--r--r-- 1 root root 4096 Nov 27 04:29 present > -r--r--r-- 1 root root 4096 Nov 27 04:29 serial_number > -r--r--r-- 1 root root 4096 Nov 27 04:29 status > lrwxrwxrwx 1 root root 0 Nov 27 04:29 subsystem -> > ../../../../../../class/power_supply > -r--r--r-- 1 root root 4096 Nov 27 04:29 technology > -r--r--r-- 1 root root 4096 Nov 27 04:29 temp > -r--r--r-- 1 root root 4096 Nov 27 04:29 type > -rw-r--r-- 1 root root 4096 Nov 27 04:29 uevent > -r--r--r-- 1 root root 4096 Nov 27 04:29 voltage_min_design > -r--r--r-- 1 root root 4096 Nov 27 04:29 voltage_now > > as i read it, what i'm interested in are those early "start" and > "end" threshold variables which are, respectively, on my system: > > $ cat *start* > 75 > $ cat *end* > 80 > > as i read it, that defines a very narrow window such that, if the > battery charge drops to 75%, it will start charging, and it will stop > charging once it reaches 80%. in other words, if i leave the laptop > plugged in the whole time, battery charge will bounce back and forth > between 75% and 80%, am i reading that correctly? > > i ask since, with those values, my battery was at 82%, i plugged in > the laptop, and it proceeded to charge .. 83% ... 84% ... not what i > expected. > > am i missing some other config setting, perhaps one that activates > that feature? > > rday > > To unsubscribe send a blank message to linux+unsubscribe [ at ] linux-ottawa [ dot ] org > To get help send a blank message to linux+help [ at ] linux-ottawa [ dot ] org > To visit the archives: https://lists.linux-ottawa.org > >