The ReVIVE solar power charger is highly portable and easy to use. I’ve tested it and can charge an iPhone twice with it on a full charge. If you charge it by solar only, it has a 50% charge, which is enough for one iPhone charge. With the extra two panels, it’ll charge in 2 hours which means, given enough sunlight, your cell phone will always be charged. This could prove crucial in emergencies.
The photo shows the charger unit with two extra solar panels. Everything easily snaps into place and it folds up neatly to about the size of a paperback. Total cost is $85 from Amazon.