The Belkin BoostCharge Pro Fast Wireless Charger for Apple Watch + Power Bank 10K is a capable battery pack, but it's not cheap.
Belkin Boostcharge Pro Portable Wireless Fast Charger For Apple
Belkin BoostCharge Pro
Belkin BOOST↑CHARGE™ PRO 2-in-1 Wireless Charging Dock with
Belkin BoostCharge Pro Fast Wireless Charger for Apple Watch +
Belkin BOOST↑CHARGE™ PRO 2-in-1 Wireless Charger Stand with
Belkin Boost Charge Pro review: My favorite bedside charger
Belkin Boost Charge Pro 3-In-1 Wireless Charging Pad For iPhone
Belkin BoostCharge Pro 3 in 1 Wireless Charger with MagSafe
Belkin BOOST↑CHARGE™ PRO 3-in-1 Wireless Charging Pad with
Belkin 3-in-1 Wireless Charger with MagSafe Charging 15W, Black
Belkin BoostCharge Pro Fast Wireless Charger for Apple Watch +
Belkin BoostCharge Pro Fast Wireless Charger Apple Watch Power
Fast Wireless Charger for Apple Watch + Power Bank 10K