Have a brand new/refurbished N900 here, a replacement of my broken phone.

Turned it on, had some very odd charging issues. It was jumping from saying 'full' to saying 'battery low' etc. so I left it to charge overnight. The next day it's fine, aside from this:

It keeps saying 'Not Charging' when it's not even plugged in to anything. This is a very strange error, and I just hope it isn't another hardware malfunction.

I've searched for help to no avail.

Thanks in advance,
K