Why doesn't pin 19 work when powering the EzSBC Esp32 board from batteries?
There is a subtle design choice in this board that took be hours to figure out.

According the connection schematic the blue leg of the LS3528RGB LED is connected to IO19 through a 1k resister (R2-1).  However the power leg is connected to Vusb not 3.3V like the other RGB LED.  This means that the LED connected to IO19 is only usable when the board is connected through the micro-USB port and not when connected directly to battery.

This can be useful for programmatically reading whether the board is running on battery or USB.