A charger is provided for charging a battery from a source and capable of detecting and switching polarity. The charger includes a first detection block for connection with the source, a second detection block for connection with the source, a first switch connected with the first detection block, a second switch connected with the second detection block and a switch actuation block connected with the switches and for connection with the battery. The switch actuation block includes a first relay and a second relay. The first relay is turned on for sending power from the source to the battery when circuit flows through the first detection block and the first switch. The second relay is turned on for sending power from the source to the battery when circuit flows through the second detection block and the second switch.