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I have a ThinkPad T420s and would like to expand the battery service life (not maximize time the laptop can run off a battery)

I have tp-smapi-dkms and sysfsutils installed, and when I run:

$ ll /sys/devices/platform/smapi/BAT0
total 0
drwxr-xr-x 2 root root    0 Sep 12 08:00 ./
drwxr-xr-x 5 root root    0 Sep 12 07:59 ../
-rw-r--r-- 1 root root 4096 Sep 12 08:15 barcoding
-rw-r--r-- 1 root root 4096 Sep 12 08:26 charging_max_current
-rw-r--r-- 1 root root 4096 Sep 12 08:26 charging_max_voltage

...

-rw-r--r-- 1 root root 4096 Sep 12 08:15 power_avg
-rw-r--r-- 1 root root 4096 Sep 12 08:15 power_now
-rw-r--r-- 1 root root 4096 Sep 12 08:15 remaining_capacity
-rw-r--r-- 1 root root 4096 Sep 12 08:15 remaining_charging_time
-rw-r--r-- 1 root root 4096 Sep 12 08:15 remaining_percent
-rw-r--r-- 1 root root 4096 Sep 12 08:26 remaining_percent_error
-rw-r--r-- 1 root root 4096 Sep 12 08:15 remaining_running_time
-rw-r--r-- 1 root root 4096 Sep 12 08:26 remaining_running_time_now
-rw-r--r-- 1 root root 4096 Sep 12 08:15 serial
-rw-r--r-- 1 root root 4096 Sep 12 08:17 start_charge_thresh
-rw-r--r-- 1 root root 4096 Sep 12 08:15 state
-rw-r--r-- 1 root root 4096 Sep 12 08:00 stop_charge_thresh
-rw-r--r-- 1 root root 4096 Sep 12 08:15 temperature
-rw-r--r-- 1 root root 4096 Sep 12 08:15 voltage

So there should be start_charge_thresh and stop_charge_thresh available, I can set when the battery stops charging with:

$ echo 80 | sudo tee /sys/devices/platform/smapi/BAT0/stop_charge_thresh
80
$ echo 80 | sudo tee /sys/devices/platform/smapi/BAT0/stop_charge_thresh
80

But setting when it should start charging fails:

$ echo 40 | sudo tee /sys/devices/platform/smapi/BAT0/start_charge_thresh 
40
$ cat /sys/devices/platform/smapi/BAT0/start_charge_thresh 
cat: /sys/devices/platform/smapi/BAT0/start_charge_thresh: No such device or address

How is this possible? I am running out of time.. when I plug in the adapter it still isn't charging!

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2 Answers 2

Reset to default
4

please take the following steps and remember backup your configuration before you do anything:

sudo modprobe tp_smapi
lsmod | grep smapi
sudo echo "tp_smapi" >> /etc/modules
sudo echo "devices/platform/smapi/BAT0/start_charge_thresh = 40" >> /etc/sysfs.conf
sudo echo "devices/platform/smapi/BAT0/stop_charge_thresh = 80" >> /etc/sysfs.conf
sudo service sysfsutils start

reboot your device and check it out!

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2
  • I know it's been a long time, but could you elaborate your answer a little? I have the same problem as the OP, but I don't understand at all what these changes are supposed to do. Thanks.
    – bgusach
    Apr 16, 2016 at 16:58
  • This won't work, obviously. Doesn't matter if you set it from console or in some config file when the threshold doesn't work at all… See my answer :)
    – helb
    May 10, 2017 at 8:20
1

The thing is, T420 and some other Thinkpads have the start_charge_thresh broken/crippled somehow (https://github.com/evgeni/tp_smapi/issues/3).

I solved it by using tpacpi-bat instead of the tp_smapi module: https://github.com/teleshoes/tpacpi-bat

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