I have one of these and it works great! However be AWARE.... there are some models around which use a questionable controller chip... some versions over drain the battery, others over charge but there all look the same case-wise, you only know when you check the PCB inside.
Sorry I can't find the thread right now but on some other forum there is a 10 page thread on these things, think its on a flashlight forum. Just google "power bank 18650" or something, you'll find it.
As for mine, I snipped off all the clips on the lid, glued some super small rare earth magnets to it and now it works great. I took the clips off as you will near wreck the thing getting the lid off!