I needed a portable charger on the go, so i syumbled upon this little guy, one thing that cought my eye was it can charge 21700 batterys, and i dont have a charger for that, it can also charge 20700 and of course 18650 all at 2A wich is super fast, you can aslo charge a phone with it also, it does seel to hold a flat top cell better then a button top, all in