Just ordered a Zenfone 2 to replace my old S3. Love the phone, but hate the non-removable battery. Took the leap anyway because of the price. What are your best recommendations for battery backup units in the ~6000 mAh, ~12000 mAh, and ~20000+ mAh ranges? I figure I can snag a small backup that can fit in a pocket and a larger one I can leave in my car/bag/backpack. Which ones have you guys experienced that are long lasting and charge effectively? Ones that are resilient? Anything to the gimmicky seeming solar charging backup units from the like of ZeroLemon or another producer?