A portable backup charger includes a set of batteries; a charging circuit; a charge-discharge protection circuit; multiple DC-DC voltage adjusting circuits including a DC-DC 19 V-output boost circuit, a 12 V output circuit, and a DC-DC 5 V-output buck circuit; a MCU circuit; a 12 V output circuit outputting a current in the range of 100 A to 400 A; and a 150 A-250 A fuse. The set of batteries is composed of lithium iron phosphate batteries and lithium cobalt oxide batteries. The 12 V output circuit outputting a current in the range of 100 A to 400 A is directly connected to the set of batteries without interference with the charge-discharge protection circuit. The charger is convenient for carrying, and is capable of providing power for different electrical instruments including for an automobile.