Debian and Ubuntu power management

Question

I use Debian normally, but whenever Ubuntu releases a new version I tend to use it for some time.

In the newer version a lot of changes have been made. In Ubuntu I observed that the backup battery shows 2.15min but the same in Debian shows 1.40min. Can anyone explain why there is a difference?

Answer 1

I suspect there is not a definitive answer. While the amount of charge of a battery is a definite, known quantity, passed to the computer by the chip on the battery, the estimate duration of a battery charge is done by dividing that quantity by the average energy consumption for a given unit of time.

It might well be that your debian and ubuntu installations have a different record of your battery usage history (e.g. they have a different record of how much energy you typically use in one unit of time).

In some cases it's possible to make the measurament more accurate by actually doing a couple of complete cycles (full charge -> full discharge) while using the computer normally.

An experiment you can do is to actually check if the actual duration of the battery is the same under debian and under ubuntu. Should you find that is not the case, than you would know it's not a difference in the recorded data, but some difference in the system configuration that brings to an actual different power usage.

If you will do any of these test, I would be very much interested to hear what was the outcome, as I am a GNU/linux user (various flavours) too!

Answer 2

Like mac said, the estimate remaining battery time is calculated from the average energy consumption of the computer.

What you can do is check under /proc/acpi/battery in each OS. Check for files called info and state and compare the results on both OSes. This should give you a hint on why the results are different.

Answer 3

Ubuntu makes some changes that in Debian are left to the user. However the biggest thing is likely to be that Ubuntu has a newer kernel and other software - there's been a lot of work in reducing power consumption recently. What version of Debian are you using, stable or testing/unstable? PowerTOP can be used to see what's causing your CPU to wake up (and hence use energy). That site also has a list of other things that can be tuned to save power.