Amazon.com: Anker PowerCore+ 20100 USB-C, Ultra-High …

This battery works amazing with the Nintendo Switch. I plugged it in at around 64% battery on my Switch. Played for three hours, and at the end of my play session I was at 94% on the Switch and around half capacity left in the battery. Be sure to turn on the battery first (pressing the power button) and hook it up to the switch USB-C to USB-C.

https://www.amazon.com/Anker-PowerCore-Ultra-High-Capacity-Portable/dp/B014ZO46LK