ca long time I hesitated to invest in a backup battery for my laptop devices. I started for this one after reading a test. I am amazed by its charging capacity, as well as mobile phones computer by USB. Too bad it does not work on my tablet that has a proprietary charger. I did not have accurate test but must make several full charge of smartphone without much problem.
Attention however to the size and weight which will appear in a light bag but will be bulky for a pocket.