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.