1

I'm using Ubuntu 18.04 and TLP (Linux Advanced Power Management).

When I have my laptop plugged and battery inserted and TLP is in auto mode (it detects the cable and goes AC mode), the CPU temperature is on average 20°C higher than if I force the system to go to Battery mode (and plugged) by doing

sudo tlp bat

Why does that happen?

For example, I turn on the computer, so TLP is in auto mode. I type

sudo tlp-stat -t

to get the CPU temperature and it's around 70 °C. If I type

sudo tlp bat

it goes down to around 50 °C. If I make it go back to auto/AC (it's plugged) mode by typing

sudo tlp start

or

sudo tlp ac

the temperature goes back to around 70 °C.

1

Battery mode of tlp is configured to save power.

When you use less power, less power is wasted to be turned into heat by the inevitable inefficiency of the device (see the Second Law of Thermodynamics).

Therefore, things are cooler. More general information is available in this link and many others which discuss CPU Power Management.

| improve this answer | |
  • Does that mean being in Battery mode is always better since it avoids overheating? Does using less power mean lower performance? I don't know if this is right, but when I'm in Battery mode but still plugged, there is no discharging (at least it keeps showing 100%) as if it was in AC mode. I thought that the Bat mode would "turn off" the energy from AC – Rule184 Mar 26 at 22:50
  • 1) Define 'better'. 2) Less power does mean lower calculation and graphical performance, i.e., 'slower'. – K7AAY Mar 26 at 22:58
  • Well, since both modes keep the battery charged, then I'm not wasting battery cycles, and in Bat Mode I'll have less damage to the hardware for not overheating. Since I usually work with my laptop plugged, I'm asking if it's better to always keep it on Bat Mode. Given (2), maybe I'll turn to AC Mode only if I really need better performance. – Rule184 Mar 26 at 23:13
  • Constantly trying to push more electrons into a lithium-ion battery once it reaches 80% results in shorter battery life. Many Windows battery control apps recognize that, if if your PC is left plugged in most of the time, some will not charge the battery up all the way. :Most Linux utility coders seem to believe More (Charge) is better. – K7AAY Mar 26 at 23:17

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