The external charger and batteries thing is not a permanent solution as I found to my detriment. First it is very frustrating having to change batteries everyday. Some may not mind but I got really tired of it.
More importantly what if the usb port finally dies? With the N900 it is almost certain you will need to reflash at some point. I was using the external charger and spare batteries for three months but then I bricked my device. If I was out of warranty I would have been left with a $625 brick.