i am actualy facing the exactly same problem now.
i also had this problem before.

i have 2 batteries and long time ago batteryA started to stop charging anymore. just few weeks ago, when i tried batteryA again, it charged and worked.

just few days ago, i left my N900 unused and now both batteries and the N900 are having the problem as mentioned in the beginning of this thread.

i searched and didnt have to create new topic
hope someone can provide explanation, if not solution.