Thanks for the input, I think I am going to keep my eyes open for a good deal on a solio.

@LordRaiden: Thanks for letting me know about that pull-charger. I've been hoping for something just like that. I hope they get their funding and start making them soon.

Solio owners: The Solio has a 1800 mAh battery, and the Nokia N810 has a 1500 mAh battery. So does the Solio have enough juice to fully charge an N810 with a dead battery? In other places, I have read that emergency cell chargers that take 2 AA batteries can't fully charge an N810 from dead, even though AA batteries range from 1700-3000 mAh (according to Wikipedia). This makes it seem like the Solio's battery shouldn't be big enough... or is there something that I don't understand about the way this all works?

The battery capacity issue is always a problem, but I used a solio for an entire summer to charge a phone (it was an experiment), but worked wonderfully. I would certainly recommend it for anyone. When I travel I charge mine up prior to leaving (not in the sun) and make sure it is fully charged. It will stay that way for many weeks, and is "always available" and can be topped off quite easily.

So what exactly are the requirements of any given charging device to charge an n800/810? It doesn't necessarily have to fully charge but what is the minimum power requirements to start charging?

Minimum power requirements are 5v @ 300ma. The charger circuits won't kick over below that, and if they do, you risk damaging them. 500ma is standard usb current. 890ma is the output of the travel charger by Nokia. All are @5v. You really don't want to go beyond 900ma when charging the NITs since you could damage the charging circuits.

What I've found very useful for charging devices while traveling is the Tekkeon MP1550 as it can use either rechargable AA's, or it can charge them from a usb port on another device. So it can charge your nit, or your batteries. And on the odd chance you can't get anywhere and charge your rechargeables, you can just buy a pack of batteries from the local 7-11 and use those instead. So it's very flexible.

It's not as compact as the Solio or some other battery pack systems, but for 90% of situations it's perfect. Now if you're going out camping away from civilization, or you'll be traveling for long periods with little hope of finding AC power to recharge your batteries, then I highly recommend the Solio. For everything else, the Tekkeon MP1550.

AFAIK the chargers are about 5.2V, so slightly above 5V. If you keep your voltage at that level there's no reason to worry about the current, the charging circuitry in the tablet will take care of that. The way to damage the device is to crank up the voltage beyond what the charging circuit can handle.

EDIT: The idea about a hand-cranked charger isn't bad in itself, as you should only have to provide an output of a few watts to charge with the maximum current the device can handle. The problem is really that you can't charge it directly like that, it would take two hours.. so, what you want is a hand- (or foot-)cranked charger with a built-in _big_ battery which can take being charged with several amps. Then get on your pedals and give it 50 watts for a while, it'll be demanding but still just a tenth of what a pro biker puts out! Then charge your NIT from that battery over the next couple of hours.

Actually, the travel charger is spek'ed out at 5v.
The ones that have an internal capacitor also work very well. The advantage of the capacitor version, although slightly more expensive and harder to find is that you don't have to work as hard to get your final charge as the amount of wasted power on a capacitor based model is nearly zero whereas you loose some voltage to heat and other issues when using a battery based unit. Plus capacitor based models don't loose their charge.

Umm no. I can fully charge my Solio on less than 1 day's direct sunlight. yes the Wall charger is faster but then we expect that.

I don't have an 810 so I can't speak on that battery but my N800 it will take 2 "blinks" (out of 4) of the charge to top off my tablet starting from the low battery warning.

Therefore you're looking at 2 "full" charges from one fully charged solio. That's the Solio "sunflower" classic design and not that new flat plate design.

I have the little Freeplay radio with a hand-crank. I've tried using it to charge my N800 directly (using the adapter tip from my Power Monkey Explorer). It does seem to work, but for short-ish cranking sessions, the fact that the N800 kept waking up and displaying popups about charging status made me think the net gains weren't too high. For sustained bouts of charging directly, it is probably OK. I assume that charging the N800 whilst it is on is the optimal solution to avoid wasted power during a boot phase.

Instead of charging directly, I've resorted to charging the Power Monkey battery directly from the Freeplay crank, and topping it up with what passes for sunshine in the UK using the Power Monkey's solar panel. I can then charge the N800 from the Power Monkey battery when it needs it.

My experiments at self sufficiency haven't been that extensive though. I could only be bothered to keep the N800 going in this way for about 10 days, with perhaps 30 minutes web browsing, periodic email transfers and downloading and listening to a couple of podcasts each day. With a bit more sun, and a better positioned solar-cell, and some top up charging with a crank, I reckon this would be sustainable, but I suspect that hitting the battery hard with daily viewing of streaming video or other heavy/continuous processing would be would give you RSI trying to keep up with the hand crank. The wind turbine might be better suited to the UK climate, so I am tempted to try one out.

fnord