So, earlier today I connected my N900 to the wall charger (the battery was at about 20% at that time) and discovered that it was not charging; because I had unplugged the charger from the wall after the last charge; so I plugged the charger into the wall, and left the phone to do it's charging.

I came back an hour or two later, and saw that the notification light was solid orange on the phone, so I slid the keyboard open, only to have nothing happen.
I was able to turn the phone on, and then remove the usb cable, and discover that the phone was down to a charge of 4%.

How could this happen?
See the attachment for the battery log.

Could it be because I connected the charger to the phone, and then to the wall?
I just got this phone last week, so I probably did something wrong..

This post from another thread may helps you: