We take a familyworth of phones and tablets on holiday and there just isn't enough hours in the day to keep them all charged - especially in a hotel where the electricity goes off when you go out. If we are out all day and evening it's impossible to get them all recharged overnight.
Here I found a solution - the sun

Not too scientific but from full charge I charged a 21% battery iPhone and a completely drained and off iPhone off one charge. It has 4 blue LEDs when fully charged and went down to one after charging the two phones. It has sat on my window sill for 2 hours and is back up to 3 out of 4 - and that is in grey, overcast Scotland - I can't wait to get it into the sun somewhere abroad

Twenty quid, it's brilliant.
http://www.amazon.co.uk/gp/product/B00J3K5VKW/