Here is a portable power bank for your smartphone that doubles as a charger for your Apple Watch. The Tripp Lite Portable Charger for Apple Watch comes with a Lightning connector. It also has a USB output and wireless charger. Its Lightning cable delivers 5V 2.4A charger for your Apple devices.
This portable battery bank has 5200mAh battery. You can use this to charge 2 smartphones or tablets and Apple Watch on the go. You can find out more about it here.