Whilst others have answered the question... if you currently have an N900 with a limited amount of charge, and unless you have a means to recharge your battery without it, you may get further by dumping any important data to a microSD card instead of fetching it over Wifi.

That depends, obviously, on how much data you are talking about - if it's trivial, then WiFi is fine. Can I also suggest, if you're replacing or repairing the N900, that you might wish to install and use BackupMenu to produce a backup of your rootfs and optfs to an SD card; that will let you restore the OS and settings to a fresh (or repaired) N900. It does not, however, backup /home/user/MyDocs, so preserve your own files manually.