Battery cooling unit and battery cooling system

Provided is a battery cooling technique capable of cooling the entirety of a battery. The battery cooling unit (40; 40A; 40B; 40A, 40B; 40C); 40D) includes an inlet port (41) into which a heat medium flows, an outlet port (42) from which the heat medium flows, a plurality of heat exchange parts (51-54) thermally connected to the battery (Ba), and a distribution flow path (60) for distributing the heat medium flowing in from the inlet port (41) to the plurality of heat exchange parts (51-54). The distribution flow path (60) has: a flow dividing section (61-63) that divides into an introduction path (71-73) through which a part of the heat medium that has flowed in from the inlet (41) flows to the upstream heat exchange section (51-53), and a bypass path (66) that bypasses the upstream heat exchange section (51-53); and merging sections (81-83) that merge the heat medium flowing through the upstream-side heat exchange sections (51-53) and a part or all of the heat medium flowing through the bypass path (66), an