Hi guys. What external battery packs are you using? Can you please share your experience with it? I have a big problem with the short battery life of my phone. I'm looking for an external battery pack and find tons of them, capacity from 2600mAh to 20000mAh and many at cheap price, when I go through Amazon and Ebay. I'm not sure about how fast will these battery packs charge. And it's hard to decide which to buy. Anyone can suggest?