Abstract: An electricity storage device and a portable electric-powered tool. The device comprises at least a battery; at least a super capacitor, which has lower internal impedance, when fully charged, than that of the battery and connects the battery in parallel; and an output end for supplying the electricity. The super capacitor is the major power supply for the pulse current output; the battery is used for generating electricity to the super capacitor and is the secondary power supply for the pulse current output. The connection of the battery and the super capacitor does not need any converters or current-limiting resistors.