It's essentially a power bank that has a usb-c connector directly into the device.
Nintendo of Japan made a little writeup about using power banks. Translated on reddit.
- before charging the Switch with a power bank, users should “always perform the latest system update”
- if you would like to charge your system with a power bank, you should use the official USB charging cable
- if using a third party option, use a USB charging cable with a 56k Ohm resistor
- charge the Switch in an environment where the temperature is between 5℃ to 35℃ (41°F to 95°F).
- charge your Switch at least once every 6 months
- if the system isn’t charged for a long period of time, surplus electrical discharge may damage the console’s ability to charge
- repeatedly charging the Switch will slowly reduce its overall battery life over time
- if your Switch fails to charge or it has a very short battery life, you will need to replace the battery by contacting Nintendo
Source:
https://www.reddit.com/r/NintendoSw..._japans_support_page_gives_details_on/dwn4x23
For the most part,
do not use any third party power banks and battery packs that connect directly to the device.
Edit: I just noticed... that power bank case you linked covers the console's exhaust. From the get-go that is a dangerous and terrible case for your $300 device.