A battery pack thermal management system can include a battery pack including a plurality of battery modules encased within a battery case, a coolant line having an inlet and an outlet each penetrating a perimeter of the battery case and at least one thermally activated valve. The at least one thermally activated valve can be configured to spray coolant onto one or more battery modules responsive to a temperature within the battery pack exceeding a temperature threshold. The temperature threshold can be defined based on the temperature of a thermal event occurring within the battery pack which exceeds a normal operating temperature of the battery pack. The coolant line within the battery pack is biased towards the perimeter of the battery case. The battery pack can power a battery electric or hybrid electric vehicle.