The fuse is 3 amp according to a manual I found.
I do not know what the battery is.
I doubt it is a fuse problem as it looks like it would kill power to the control board.
I think it is the control board because the unit runs OK until the evaporator coils freezer over due to no defrost so the freezer and fresh food thermistors must be OK.
Also since you can force a defrost the wiring to the defrost thermostat and the defrost heater must be OK.