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European iPhones are more fun now
(www.theverge.com)
This is a most excellent place for technology news and articles.
The space used by the smallest solar charger I've seen on Amazon seems to be similar to 6 or more batteries in the format the N900 was taking - so if you look at space, slow charging from solar charger, and reliance on sun conditions taking individual batteries seems to be the better option for a few days hike. It's also easier to stow individual batteries to wherever you still have space left.