It might seem a little bit strange to recommend a product that doesn't work out of the box with the N900, but that's exactly what I'm about to do.

USB external chargers have moved on considerably in the lifetime of the N900, so I recently bought myself a TeckNet iEP380-II 7000mAh pack, via Amazon. It doesn't conform to the USB dumb charger spec, like many external packs, so you'll need a Proporta cable for it to work with an N900.

Once that's sorted, though, there's much to like. The pack uses a microUSB charging port, so it charges from existing N900 chargers, and it uses microUSB as its default cable too, so it comes with a bunch of adapters that also fit any of your N900 chargers. Very practical indeed, no additional cr*p needed for charging the pack over and above what you'd carry anyway.

Two ports capable of 1A output, haven't fully tested how fast it charges the N900 yet, but means I could, if needed, charge both phone and headphones from it at the same time.

The capacity feels subjectively about right, we'll see, it's not as big and hefty as the 11000mAh packs but should still be able to rescue the N900 two or three times off a single charge. It may not be perfect, but combined with a Proporta cable it seems to be a distinct improvement on most of last year's products, so I thought it deserved a mention here.