Self made are nice but ideally you want something with at least 5 (6V) or 6(7.2V) rechargeable AAs and use a 5v regulator so that you obtain a better charge throughout the load on the batteries. Of course it costs more and the regulator will eat up some of the power.

Excellent news Saves me typing something up. Thanks for that!

I bought this: Proporta TurboCharger 3400. Just got it delivered, comes with plugs for nokia/apple/microUSB and a few others. A quick test showed it charging my n900 fine. I'll do a full test when I've got the charger fully charged and my n900 drained (shouldn't be too long then )

That looks very much like the one I got from http://portablepowersupplies.co.uk/ for £22 shipped to Sweden (although admittedly only with the micro-USB tip, 8 tips can be had for £4.50).

wow yeah, they look exactly the same besides the colour. I'm going to be stuck in Paris CDG for 10 hours on Sunday so I'll definitely see if the investment is worth it then.

ok so i fully charged the proporta 3400 (took 4 hours).

I then charged my nokia 6610 navigator (BL-5M 900mAh) from low battery indication to full in 1.5hours.

The proporta was left with 4 LEDs on.

Then I fully charged my n900 from the first low battery indication and this took 2 hours.

The proporta was left with 1 LED on, I don't know how accurate the indicators are but 1LED works out to 680mAh if the device is to spec.

Note: I received a 7minute phonecall inbetween the n900's charging, I disconnected the charger and plugged it back on afterwards (3g and wifi were off)...

Not the most comprehensive test, but by these numbers I rate the proporta 3400 should give the n900 2 full charges with the device on and minimal usage during charging. Good enough for me!

Does anyone have any thoughts on this sort of thing: http://www.paramountzone.com/rphone.htm ?

hmm, if two minutes of winding gives you 10mins on an ipod then you'll be doing plenty of winding for your n900

Thanks for that. I was kind of expecting "will / will not destroy your device" thoughts, but nonetheless quite an interesting one... (Think of the CO2 emissions though! )

It certainly won't destroy your device anyway. As said, it'll take a lot of winding to get any real power, so I suspect it'll only be useful for emergency situations, rather than for regular charging. Unless you're trying to build up your arm muscles anyway!