Having tried my 2nd N900 (which was off) which worked, I swapped them over and my N900 still didn't charge. I restarted it, and it charged when off. It then booted and continued to charge. I then unplugged it, waited for the bank to deactivate, then plugged it back in and it now charges.

BME glitches I suspect. Incidentally, it was plugged into a wall charger overnight and my morning alarms were mixed in with low battery beeps. It does this occasionally, really quite annoying. Cheers for the help though!

PS, the bank has charge two ports, a 2.1A one and a 1A one, very snazzy