I just use an external battery pack, the predecessor to this one:

http://www.amazon.com/GearPower-Port...8592231&sr=8-2

Instead of charging off a computer, I usually use a little AC USB charger, like this:

http://www.dealextreme.com/details.dx/sku.19242

Works great. Simple. Small to carry. On airplane trips, I leave the external battery connected; I don't know if that's more efficient or not.

Have a good trip!

This device is very nice
http://europe.nokia.com/find-product...specifications

I don't believe there is an external portable charger that will provide you 3 days work-time.

You don't have to use your N810 in order to charge your batteries - you can use a separate charger and charge them simultaneously - these chargers are also cheap.

thats right... but If there are 4 one-way AA Batteries inside which can be changed it should work. Back in civilisation after 3 days I have to buy new ones... Not eco-friendly I know... But an acceptable solution for for exceptional circumstances.

I`ve never seen an external charger for a BP-4L battery. But you are right - http://cgi.ebay.de/Akku-Ladeger%E4t-...100312138004r5... Now the parts for my diy-project are ordered. Doesn`t matter... I surely will have fun building it

Another possibility could be this: http://nokiaport.de/index.php?mid=5&pid=akkuersatz - on this site is a circuit diagram for externaly powering Nokia devices without a battery inside. Do you think that it ist possible to use 3 AA reuseable AA batteries with 1,2V (maybe a bit more...) each - 3,6V together and this diagram but without the diodes D1 and D2? Or will the current be to high without the low drop regulator?

There is no way 4 AA batteries could provide enough work time because most of the energy will be used to charge the battery inside the N810, so it will go in the air as temperature. For example the Nokia emergency charger (a link was given before in this theme) is 1500MAh (i.e. = the BP-4L) but provides only 3 hours work time (according to the official specifications). However, (see below)

I didn't know that such things exist. I can not tell anything about the diodes but if you manage to somehow use directly AA or other batteries with no battery inside N810 then I think you will have good work time because all energy will be used by N810.

I just contacted the author of this article. He`s sure this works for every Nokia device. The 75k resistor makes the device think that there`s a Nokia battery inside. The 2 diodes are only neccessary if the input voltage is 5V - so that the output voltage is about 3,7V. I will try this, too...

I've found that my MP1550 doesn't do a very good job of charging my n810, as with any other USB based charging device.

notnarb, you need a decent set of rechargeable batteries in it. If you use off the shelf AA's you will only get about a 50% charge before the MP1550 dies. And it's not the charger's fault. Normal, generic AA's just don't have the umph to do the job. It's why I switched to using 2500mah NiMH batteries in mine. One set of those is enough to charge the NIT from dead to 100%. And if you look at the numbers, 2500mah at 1.2 volts is about right to achieve that.

1.2v*4 = 4.8v
2500mah*2 = 5000mah / 2.5 = 2000.

The NIT battery is 1700mah. If you remove 300mah for overhead, that's just about spot on to completely recharge a NIT from dead. 2.5 is the average power to charge ratio on most batteries. It varies depending on battery type (like Lithium Ion I believe takes 2.2 times the amount, whereas lead acid is 2.9 or something like that. The way to calculate it is to determine the total amount of power needed to charge the battery from dead to full divided by the size of the battery.

I've done numerous tests myself, and the charge rate is about exactly 2.5 to 1 for the NIT at 5v, 500ma, which is the standardized bar by which I do all my testing.

Funny, I also just did some look around for an external battery-pack. And in the end I came to similar results: a 12V supply with a car charger would probably do the best job. Batteries are available in different shapes and sizes and might be tight to any part of the bike or your backpack. And when using some kind of universal car charger with many adaptors you could even charge other devices too.

Another idea would be this little thing. A solar charger with one great benefit over other solar chargers: you may line up several of them to increase power output. As usual you can directly use solar plate for charging (not recommended at night!) or fill it up with rechargeable batteries.

Downside is the price of course. 30€ for one piece and probably best useful when lining up two or three pieces ....

http://www.conrad.de/ce/de/product/200285/

Btw the small Nokia tip adapter I received with my Tekkeon MP1550 is very inefficient, atleast it gets very hot, and there's only about 250mA-300mA charge current going to the N810. I just used another tip/cable/adapter thing I got with some emergency chargers from certain chinese discount online shop, gave about 500-800mA, depending on the strength of the AA batteries inside.