I've used a few portable batteries, but for the most part the form factor didn't make sense for me. If I was going on a business trip I'd have a few hours between outlets and would generally be able to keep my phone charged and I didn't want to carry around extra weight in the form of a battery. Most days I work in a lab, but have a convenient desk outlet at the ready if I end up spending too long on my phone and need a quick recharge. In short I didn't need a battery and the batteries available didn't make sense (too big for a one time charge and not enough power for an entire camping trip etc). But I've found a real place to use a mobile battery and the New Trent iTorch is a nearly perfect form factor for it.