To provide an abnormality determination method for battery pack and a battery pack, which can securely determine whether or not an abnormal secondary battery is in a battery pack in which a plurality of secondary batteries are connected in parallel.

The abnormality determination method for battery pack includes: during charging of the secondary battery, turning off an FET for charging/discharging provided in a charging/discharging path for 250 ms (from time T1 to T2, and from time T3 to T4), then turning on the FET, and repeating the turning off and on for every 10 minutes; calculating internal resistance of the secondary battery for every 10 minutes, on the basis of battery voltage differences (ΔV(1) and ΔV(2)) of the secondary battery detected before turning off and turning on and of charging current detected before turning off, and storing the results in a RAM. When a difference between the internal resistance thus calculated and a previously calculated internal resistance stored in the RAM is greater than a first threshold, the method determines whether or not the secondary battery is abnormal by comparing a difference between a newly calculated full charge capacity (FCC) and a previously calculated FCC stored in the RAM with a second threshold.