US Patent 11637347 Electric energy storage device and electric tool system

The disclosure provides an electric energy storage device which includes four energy units with a substantially same voltage value. Each energy unit is provided with a positive electrode and a negative electrode. The electric energy storage device comprises a socket with eight independently arranged electrode terminals that are connected with the four energy units. The disclosure also provides an electric tool system using the electric energy storage device. The electric tool is provided with plugs that may be connected with the four energy units in different states, allowing the electric energy storage device to output multiple voltages.