Amazon offers the iDeaUSA 2600 mAH Portable Backup Battery Charger Power Bank with Flashlight for $7.99.
Add coupon code XC5N383E to drop the price to $4.99 Prime shipped. That’s an all time low for flashlight battery chargers and this one gets very good 4.6/5 star ratings. 2600mAh is more than a full iPhone 6/s of charge.
If you need a little bit more juice, grab this 5200mAh iDeaPower battery for $6.99 after applying coupon code IDPME44L (available in Blue or White). This has a built in MicroUSB port, 2nd USB port and LED battery indicator.
Both of these make amazing stocking stuffers.