At the Feather 32u4's heart is at ATmega32u4 clocked at 8MHz and at 3.3V logic, a chip setup that's the same as the Flora. This chip has 32K of flash and 2K of RAM, with built-in USB. The device has built-in USB-to-Serial program & debug capability with no need for an FTDI-like chip, and can act like a mouse, keyboard, USB MIDI device, etc.
A connector has been added for a 3.7V Lithium polymer batteries and built-in battery charging to make it easy to use for portable projects. A battery is not required and will run straight from the micro USB connector. If a battery is used, it can be plugged into the USB to recharge. The Feather will automatically switch over to USB power when it's available. The battery is also tied through a divider to an analog pin to measure and monitor the battery voltage to detect when a recharge is needed.