My N900 has started reporting the battery level strangely in the last few weeks...

It fully charges to green light and then Health Check reports the last charge level as something low, ranging from as low as 443mah (today) to 890mah. If I unplug an replug the charger it goes to green light after just a few minutes and then reports last charge at around the 1100mah+ mark.

The phone's battery indicator seems to go down in accordance with the last charge value and when I correct it by replugging in the charger, it definitely seems to last for longer before asking to recharge than if I don't.

Has the battery calibration failed perhaps? I know this affects more complex laptop batteries, is it the same situation here? How do I correct it if so?