For a few years in college, when I spent more time around smokers, I carried a lighter in my purse in case a friend or a desperate stranger needed to bum a light. These days, I like to re-create this helpful gesture by bringing a portable charger wherever I go. If anyone’s phone battery is low, I get to save the day — and, of course, keep my own devices from dying. As a writer on the powering beat, I have endless options in the rotation.