Personally, I'm going to use a power pack , because I can use it in different devices. Not all phones have battery cases, can't find one for my OnePlus, and only found one for my iPod touch. But, what do you guys think? I would use a battery case, but they are slower then a lot of power packs. Some power packs, they have two amps of power, but the battery case I had for my Nexus 5 was only 1amps. However, since my phone has a big battery, I only carry the powerpack when I am traveling.