The functionality of an external battery pack comes at a cost. In short, you have to remember to charge it and bring the right cables. Unlike a battery case for your phone, which you most likely charge every evening next to your bed, an external battery pack just sits in your bag, patiently waiting for you to remember it exists. Usually that happens when it’s on its last legs, right before it becomes a hunk of useless lithium-ion cells. There’s no worse feeling than pulling out your battery pack during a desperate situation only to find it dead as a doornail.