Really, the Jewel isn’t so much a battery pack as it is a Lightning cable with a battery bulge in the middle, like a snake that just ate a rat. That 450mAh battery is only good for a ~15-20% charge, depending on the iPhone model, but that can be the difference between finishing the night with a working smartphone or an inert slab of glass. And of course, it also works as a standard Lightning cable, complete with passthrough charging and data transfer. Just use code ISGHK383 at checkout to get the best price ever.
Update: We were having some trouble with this deal earlier in the week, but it seems to be resolved now.