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I have a Samsung Series 9 NP900X4C-A01US dual booting Windows 8 and Ubuntu 12.04.

On Windows 8, the battery indicator is completely correct. When I plug in my AC adapter, it says charging, and when I unplug it, it gives me an estimate of how much my battery will last.

On Ubuntu 12.04, the battery indicator remains whatever the state was at startup. That is, if I had my AC adapter plugged in during startup, even if I unplug it, the indicator still shows charging.

The laptop has a built-in battery charging indicator, and that light is correct.

This was working about a week ago on 12.04, and I don't really know what has changed since then. I did a complete reinstall of Ubuntu 12.04 and the problem persisted.

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up vote 4 down vote accepted

It seems you are a victim of a known acpi bug (see here). Some users report that powering down and disconnecting the battery (pinhole on the underside of the notebook) temporarily fixes the problem, as does upgrading the BIOS. But the problem eventually comes back. I know of no permanent workaround at the present time.

There is also a Kernel bug report about this (it is not Ubuntu specific) here.

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