How does the EPS (Emergency Power Supply) function? Does the Mega3 need to be charged to 100% capacity before it automatically shuts off, allowing power to flow directly to the freezer, and then when the main power goes out, the Mega3 takes over?

The Mega3 does not need to be fully charged to activate the EPS function. When the Mega3 is connected to a wall socket for charging and the freezer is connected to the Mega3 with the AC output turned on, the system will automatically switch to the Mega3's power supply if the wall socket loses power. All OUPES series models support this function.