not battery, not charger, then could be software.

i have seen some weird graphs with the battery monitor on my phone (once time, one of the lines on the graph went backwards in time - i.e. towards the left - and then turned around and moved forward again).

if the battery is not at fault, and the charger is not at fault then it is something in between the two that is not routing the charge to the battery. i am not familiar with the circuitry between them. you may want to ask dr_frost_dk @ http://talk.maemo.org/showthread.php...d+battery+test . he seems well versed with battery technology and the n900's battery circuitry.