A measuring method for a portable electrical energy system includes acquiring a total capacity and an initial electric quantity percentage of each battery pack, detecting a discharging current and a discharging time of each battery pack, calculating a discharging capacity of each battery pack, calculating a remaining electric quantity of each battery pack; calculating a real-time electric quantity percentage of each battery pack; acquiring an open circuit voltage of each battery pack and a real-time internal resistance of a cell unit of each battery pack; calculating a remaining electric quantity of each battery pack; and calculating a remaining electric quantity of the portable electrical energy system. This method can reduce the calculation error of the remaining electric quantity and improve the battery utilization.