A multi-battery charger for at least one rechargeable battery includes a charger case, and a multi-battery charging module. The charger case includes a plurality of electrically neutral charging terminals spacedly provided thereon, and an electric input terminal adapted for electrically connecting with an external DC power source. The multi-battery charging module is provided in the charger case to electrically communicate with the charging terminals, and includes a recharging circuitry and a polarity detection circuitry. The polarity detection circuitry is electrically connected with the recharging circuitry to accurately detect a positive polarity and a negative polarity of the first and the second battery terminal when the first and the second battery terminals are electrically connected with two of the charging terminals, in such a manner that when a correct polarity of the first and the second battery terminals is determined, the recharging circuitry is activated to properly recharge the rechargeable battery.