Update 6/12/2018: Jackery no longer makes the Jewel, but Nomad now has a similar product. Its cable is braided, and includes a silicone cable tie, and more importantly, the battery has over six times the capacity. But at $50, it’s also significantly more expensive.
Jackery makes some of the most popular battery packs around, but the Jackery Jewel is unlike anything else on the market.
The Jewel is actually a fully functional Lightning cable, but with a bulge in the middle housing a 450mAh battery pack. That means you can unplug the cable from a charger, and with the press of a button, your phone will start drawing power from the battery instead.
Granted, 450mAh isn’t a lot of juice; it’ll charge most iPhones about 15-20%. But if you move around a lot during the day, it’s nice to be able to take a little bit of power with you anywhere. I use mine a lot in the kitchen: I keep all of my recipes on my phone, but there’s not a convenient power outlet above my counter to charge it, so the Jewel lets me get a little bit of juice with minimum hassle.
The Jewel typically sells for $16-$20, or roughly 2-3 times what you’d normally pay for a Lightning cable. If you’re not the type to be bothered by a phone battery below 50%, you probably don’t need it, but it’s a relatively inexpensive salve for anyone that suffers from burning battery anxiety during the course of their day.