It never fails; you’re busy, not paying attention and have a meeting across town in an hour, when you notice that your iPhone is down to 15% charge on the battery. Simply plugging it in for 15 minutes before you head out the door isn’t going to give you enough charge to get you through the day.
Plug your iPhone in as you normally would, then open the Settings app and turn on Airplane mode at the top. Doing so turns off WiFi, the cellular radio, Bluetooth, pretty much everything that typically drains the battery even as it’s charging.
I’ve verified that this works, and works well. My iPhone charged in nearly half the time it would normally take.
I wish I could take credit for discovering this trick, but I found it at AlliOSNews.