Just have a power regulator that converts the 5V from the USB connector to the 3.3V for the rest of the board. This receives 5V from the USB connector or the battery energy (or both) and feeds them into the regulator to generate the 3.3v rail. It has the MCP1700 3.3V regulator to exchange the LM1117 regulator from the nodeMCU design, the MCP half has a approach decrease quiescent current which helps with the battery life.