Exceeding voltage on STM32 Vbat pin
VBAT pin is for a backup battery for the real-time clock built into STM32F429.  RTC backup batteries are usually non-rechargeable Lithium cells.  Their voltage doesn't exceed +3V.  CR2032 is an example of such battery.  

If your design doesn't have a separate RTC backup battery, connect the VBAT pin to Vcc.