VRTC_3V0 serves as the RTC battery backup supply, sourced from the Coin cell RTC battery via RTC battery holder on the Carrier card and it is fed to the 1.5V regulator for the VCC_PSBATT as well as the VBBAT pin of the PMIC.
If a coin cell battery is not connected to the RTC battery holder, the 1.5V regulator will not receive input, and consequently, VCC_PSBATT will not be generated.
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Please find the detailed G36M product information in the below link,