Battery cell stack and redox flow battery

Provided is a battery cell stack in which the electric resistance between a collector plate and an end bipolar plate hardly increases with repeated charging and discharging. The battery cell stack is provided with a collector plate conducted to each of a pair of end bipolar plates positioned at both sides in a stacking direction. In the battery cell stack, two members contacting each other between the collector plate and each of the end bipolar plates undergo an accelerated test satisfying the following conditions (1) to (3): (1) one cycle is defined as a period in which pressure is applied up to a predetermined pressure over one minute, the predetermined pressure is maintained for one minute, and then the predetermined pressure is returned to the atmospheric pressure over one minute; (2) the predetermined pressure is set to the atmospheric pressure + 0.1 MPa; and (3) the number of cycles is set to 18. The two members are made of such a material that the electrical resistance value between the collector plate and each of the end bipolar plates after performing the accelerated test becomes 1.05 times or less the electrical resistance value between the collector plate and each of the end bipolar plates before performing the accelerated test.