The STEVAL-FCU001V1 board with a STM32F401CC MCU needs a lipo 1-cell battery to be connected to the battery connector (BT1) for stand-alone operation according to the ST board manual. Some older ST manuals might create the impression that this battery is optional.
This is not the case. The battery must be present to be able to program and run any application on this eval board. Otherwise the power supply for the board is not sufficient even when powered through the micro-USB connector.