the connecting device 23 the voltage detecting module 12 is mainly used for measuring a voltage difference between the positive electrode 211 and the negative electrode 221 the control module 13 is electrically connected to the voltage detecting module 12 and the display 14 and used for computing an equivalent resistance between the positive electrode 211 and the negative electrode 221 according to the load current and the voltage difference measured and the ohm 39 s law formula v i r in addition the control module 13 can make the display 14 to show the information related to the battery module 2 a such as the computed equivalent resistance mentioned above more detail the voltage detecting module 12 can further include an analog digital converter 121 a millivoltmeter 122 an analog scanning switch 123 and a plurality of detecting ends the plurality of detecting ends can be disposed on the battery module 2 a the load 3 and any point on the circuit via a detecting end locking device 126 to form the voltage monitoring points in practical applications the detecting end locking device 126 can be a screw to lock the detecting ends on the electrodes or other contacting points or any other kinds of holding devices the millivoltmeter 122 is used for measuring the voltage difference between the detecting ends or the voltage detecting points the analog scanning switch 123 is used for switching the detecting ends measured by the millivoltmeter 122 the analog digital converter 121 is used for converting an analog signal measured by the millivoltmeter 122 into a digital signal and transmitting the digital signal to the control module 13 the plurality of detecting ends includes a first detecting.