Just a Tip: I Have The Power!
Cell phones have grown from being essential communication tools to supercomputers in our pockets that we're inseparable from and are linked to every aspect of our lives. They can be especially essential during a con as your way to keep in touch, track panels, take photos, post to social media, and navigate you to some five-star pizza. When your phone is dead, it's not just inconvenient, it can seriously hamper your weekend. The easiest way to prevent this would be to keep your phone plugged in all the time, but that's impractical for all the walking and events to attend. Taking a charger in your bag/pocket/ battle armor, however, is always a good call. Everyone needs a break for food or to rest your aching feet, and you can plug in to a free outlet while you recharge yourself. For those that can't afford to slow down, a number of companies offer external or back-up batteries. They're pretty portable, and just plug into your power port. Although designed for use when you hit critical, I'd suggest you treat them like a reserve fuel tank. Start the day with a bulkier phone, and you can downsize once the reserve runs out!
We all know the pain of a dead battery. Hopefully a little forethought will save you a heap of worry!