In a method for detecting abnormality in a parallel battery-connection circuit, the parallel battery-connection circuit includes: a first circuit including a first plurality of batteries connected in series and a second circuit including a second plurality of batteries connected in series; wherein: at least one of the first plurality of batteries is connected to a first temperature detection section, at least one of the second plurality of batteries is connected to a second temperature detection section, and the first temperature detection section and the second temperature detection section are connected to an abnormality determining section for determining abnormality in the parallel battery-connection circuit, the method comprising the steps of: detecting a first temperature of the at least one of the first plurality of batteries by the first temperature detection section; detecting a second temperature of the at least one of the second plurality of batteries by the second temperature detection section; and determining abnormality in the parallel battery-connection circuit by the abnormality determining section based on a temperature difference between the first temperature detected by the first temperature detection section and the second temperature detected by the second temperature detection section.