I have checked the pin out by comparing it to the board markings on the Adafruit Feather 32u4 board and they look to match.
So if you orientate the Meadow board with the USB connector to the left and then compare the pins to the 32u4 board in the image on the page above, the pin mapping looks to match with one exception, we have a digital pin
D02 where the 32u4 board has a
GND pin. I notice on the OLED board the
GND pin is marked as not connected so this should not matter.
Battery, you are right about the battery connector. Meadow is designed to match the Adafruit specification. You need to make sure you get the polarity correct when connecting a battery.