The utility model provides an internal resistance of cell's device is measured to loss -of -charge method, its structure includes: a plurality of measurement terminal, a plurality of transfer relay that discharges, big current discharge resistance rm, little current discharge resistance rs, current sensor and voltage sensor, big current discharge resistance rm is parallelly connected with little current discharge resistance rs again after establishing ties with the transfer relay km contact of discharging to relay contact points connection second-the 5th measurement terminal is switched respectively to the one end that allies oneself with the circuit through discharging, the parallel circuit other end switches relay contact points through discharging respectively connects first-fourth measurement terminal. Use current sensor to sample to discharge current, voltage sensor measures the battery terminal voltage. The utility model has the advantages that: 1 big current discharge resistance of per 8 economize on electricity ponds sharings, per 2 sections A series of cells discharge, the one time has been reduced to the quantity of transfer relay, very big reduction system's cost. Use one big one two kind little discharge current's mode, improved detection precision and suitability greatly.