A universal charging device and a universal charging method thereof is disclosed. An AC voltage is converted into a DC charging voltage. At least two first charging processes are sequentially performed. In each first charging process, the DC charging voltage is adjusted to be larger than the terminal voltage of a battery based on the terminal voltage and the DC charging voltage charges the battery. The DC charging voltage generates a DC charging current and a pulse current to flow through the battery until the terminal voltage is equal to the DC charging voltage. A voltage across the battery established by the pulse current satisfies a charged condition. When the terminal voltage is equal to the DC charging voltage, the DC charging current is converted into a decreasing trickle current until the value of the trickle current is decreased to a triggered current value.