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Here is how I've charged my n-gage and friends 6600 for two weeks. the cost of charger is under 40$ , handmade. It survived a 2 weeks long mountainbike trip, and charged even when riding. Currently thinking of designing a charger from a bicycle dynamo. That would charge even faster.
A panel costs about 15$. Three panels would provide around 500ma after the charging circuit. I hope that would be sufficent to charge 770.
I was looking into that product. It's a solar charger, with a battery built-in. That way, you wouldn't need sun to actually charge the 770/phone/gps. Just keep it open when you have the chance.
Also with the solio which is relevant for you is that so long as the battery has charge you can hook it into your IT and have it run off the Solio so long as there is light. So for example you can open up the classic Solio while hiking and run the IT off mostly sunlight (assuming you have it) and therefore only using the internal battery at night when you're most likely to not be doing anything that drains power. In effect you keep the internal battery as a 'ready reserve" rather than the Solio as a ready reserve.
(Linked)
, handmade. It survived a 2 weeks long mountainbike trip, and charged even when riding. Currently thinking of designing a charger from a bicycle dynamo. That would charge even faster. 