A universal charging device comprising: a charger coupled to at least one battery and configured to receive an alternating-current voltage and convert the AC voltage into a direct-current charging voltage, wherein the at least one battery has a terminal voltage when the DC charging voltage is not applied, which terminal voltage is less than a rated voltage of the at least one battery; and a power control detector coupled to the at least one battery and the charger, wherein after the charger and the power control detector determines that the at least one battery is a battery to be charged, the charger and the power control detector sequentially perform at least two first charging processes; wherein in each of the at least two first charging processes, the power control detector detects the terminal voltage, controls the charger to adjust the DC charging voltage to be larger than the terminal voltage based on the terminal voltage, and controls the charger to generate at least one pulse voltage based on the DC charging voltage, the charger applies the DC charging voltage to charge the at least one battery and respectively generates a direct-current charging current and at least one pulse current by applying the DC charging voltage and the at least one pulse voltage to the at least one battery until the power control detector determines that the terminal voltage is equal to the DC charging voltage, the at least one pulse current flows through the at least one battery to establish a first detected voltage across the at least one battery, when the power control detector determines that the first detected voltage satisfies a charged condition and the terminal voltage is equal to the DC charging voltage, the power control detector controls the charger to convert the DC charging current into a decreasing trickle current (Tl) until a value of the trickle current (Tl) is decreased to a triggered current value, and the triggered current value divided by a value of the corresponding DC charging current is equal to a fixed ratio less than 1 and larger than 0; wherein before the charger and the power control detector sequentially perform the at least two first charging processes, the power control detector detects the terminal voltage and drives the charger to provide an initial voltage for the at least one battery and generate an initial current, the initial current flows through the at least one battery, and the power control detector is configured to receive the initial current and determine that the at least one battery is the battery to be charged according to the initial current, the terminal voltage, and a charging voltage range. a charger coupled to at least one battery and configured to receive an alternating-current voltage and convert the AC voltage into a direct-current charging voltage, wherein the at least one battery has a terminal voltage when the DC charging voltage is not applied, which terminal voltage is less than a rated voltage of the at least one battery; and a power control detector coupled to the at least one battery and the charger, wherein after the charger and the power control detector determines that the at least one battery is a battery to be charged, the charger and the power control detector sequentially perform at least two first charging processes; wherein in each of the at least two first charging processes, the power control detector detects the terminal voltage, controls the charger to adjust the DC charging voltage to be larger than the terminal voltage based on the terminal voltage, and controls the charger to generate at least one pulse voltage based on the DC charging voltage, the charger applies the DC charging voltage to charge the at least one battery and respectively generates a direct-current charging current and at least one pulse current by applying the DC charging voltage and the at least one pulse voltage to the at least one battery until the power control detector determines that the terminal voltage is equal to the DC charging voltage, the at least one pulse current flows through the at least one battery to establish a first detected voltage across the at least one battery, when the power control detector determines that the first detected voltage satisfies a charged condition and the terminal voltage is equal to the DC charging voltage, the power control detector controls the charger to convert the DC charging current into a decreasing trickle current (Tl) until a value of the trickle current (Tl) is decreased to a triggered current value, and the triggered current value divided by a value of the corresponding DC charging current is equal to a fixed ratio less than 1 and larger than 0; wherein before the charger and the power control detector sequentially perform the at least two first charging processes, the power control detector detects the terminal voltage and drives the charger to provide an initial voltage for the at least one battery and generate an initial current, the initial current flows through the at least one battery, and the power control detector is configured to receive the initial current and determine that the at least one battery is the battery to be charged according to the initial current, the terminal voltage, and a charging voltage range.