Acer TravelMate 4001WLMi

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The Travelmate 4001 has a so called "smart battery" that needs to be read out like a sensor device. Unfortunately, there is no standard and portable way of doing this (although the HAL project is working on it).

Thanks to the people on the acpi-devel mailing list, Rich Townsend write a smart battery module based on the kernel EC (embedded controller) handling. It provides both a specific API, dubbed 'SBS' (smart battery system, /proc/acpi/sbs), as well as a classical ACPI compabible API (/proc/acpi/battery). The latter implies that most standard battery reading tools will just work. Good job, Rich!

For Fedora Core 5 I ported the SBS approach to the 2.6.16 kernel.

I use this with a small Perl/Tk program to produce a nice battery status indicator on my screen.

Rich went one step further by developing a way to implement the classical ACPI API completely in the DSDT, making the battery available without the need to patch the kernel. See his project web site for more details.

A word of warning

Now I can read out the battery, I can also see the astonishing speed at which the battery capacity degrades. After 6 months of use, the battery already lost 33% percent of its capacity. It seems that trying to fully charge the battery when its hot is very bad, and this notebook does not seem to do anything to prevent this from happening. In other words, a intensive use of the notebook while connected to the charger is a battery killer.
Update: After 18 months, there's only 48% battery capacity left.