When players raised concerns about how short the Wii U GamePad’s battery lasted, Nintendo moved to release a High-Capacity Battery that was easy to install and allowed up to eight hours of use.
We won’t have that option with Nintendo Switch, with the FCC (Federal Communications Commission) reviewing a production prototype design that will be used for mass production.
Their evaluation has been shared in published documents where, in SAR Test Report 01, they comment that the battery is “built-in in the EUT, and the user can’t remove the battery.”
We won’t know whether that will be a problem until Nintendo confirms how long the battery will last, presumably at the Nintendo Switch Presentation 2017.
The documents also confirm that Nintendo Switch will support Bluetooth wireless communications, won’t support 3G or LTE connections, can support 5GHz Wi-Fi connections, and will work in temperatures between 5°C (41°F) to 35°C (95°F).