"First, it's eco-friendly for our endangered earth. Moreover, I tried to charge the charger through the light in my room and it was also acceptable. So I don't need to worry there was no time to fully charge the product at all. Two USB port makes it more convenient when your friend and you want to charge the phone at the same time. The build is sturdy and it holds a lot of charge for the size.The battery is very rugged & waterproof, knocked it into my dog's filled water bowl and it still performs perfectly. The pack sat in the water bowl for three or so hours before I discovered it, no damage. Make sure to keep all the flaps secured and you won't have any problems."