The silence from replay says: It is not possible, I guess.
That's a pit, because it has industrial design with CAN transceiver, that normaly can't be used as portatile device. On the other hand STM32 has the reserved pin VBAT (that others don't) to simply connect a battery for RTC, instead you have added a complicated (and expensive) LiPo batery with charger that supplies entire MCU and shields - not an industrial design.
Please take the following into consideration if you will make another revision of this intersting board.