The Anker Powerhouse 200 is an absolute unit. It's a 200Wh battery (57600mAh) that stretches the definition of "portable," and now you can get it for $50 off from Amazon. That brings the total price down to $299.99.
The battery is equipped with two USB Type-A ports, a 60W USB Type-C port, a 12V DC outlet, and an AC outlet. Anker says it can charge a MacBook Pro over five times, and run small appliances like mini-fridges for over four hours. To charge the Powerhouse itself, there's an included AC adapter, or you can use the Type-C input.
The battery is available from the link below. Enter code ANKERPW7 at checkout to get the discount.