Very convenient, when it works ...!

It is the second that let me go .. then yesterday I'm used it. I just let it charge for about three hours, and nothing. I shake it like a dug up, and the light does not turn on. I must have bad luck, it is not possible otherwise.
It's a shame because when it works, and this little device very useful and very effective, but I admit I struggle to understand what makes it stop working well.
I hesitate to contact Anker to tell them because they will think I laugh at them, because the one I have now is the one they sent me to replace the previous ... But it will be convenient for the holidays in a few days without a backup battery!
Three stars because, despite everything, I appreciate this, but because there it is more useful to me ...