NOVELTY - The device has an impedance element (50) cooperative with a carrier (25) of a coolant activated drain plug (10). A soluble plug (15) is arranged within a cavity (20) of the carrier. A comparator circuit detects loss of continuity in the element, and provides an indication. Lines (40, 45) electrically couple the element to the circuit. The soluble plug is partially dissolved when the soluble plug is fluidly coupled with coolant so that a portion of the coolant flows between a battery housing and a drain outlet. The soluble plug is non-soluble core with a soluble polymer coating.    USE - Liquid cooled battery pack device for a rechargeable energy storage system (RESS) for a motor vehicle (claimed) such as an electric vehicle, and a hybrid electric vehicle e.g. lorry, bus, and motorcycle.    ADVANTAGE - The utilization of the drain plug allows draining of the coolant from the battery pack in the event of a crash or coolant containment malfunction. The soluble plug is partially dissolved when the plug is fluidly coupled with the coolant such that the portion of the coolant flows between the battery housing and the drain outlet, thus enabling early detection of loss of coolant into the battery following accident or related incident to avoid harm to the RESS and implementing automated corrective actions in event of detected or imminent leakage of the coolant into sensitive portions of a battery system. The device avoids an unintended electrical path or short out of the batteries or electronics associated with the battery pack.    DETAILED DESCRIPTION - The impedance element is a conductive coating. The battery housing is a lithium-ion-battery housing. INDEPENDENT CLAIMS are also included for the following:    (1) a liquid cooled battery pack    (2) a method for draining a liquid coolant from a liquid cooled battery pack for a motor vehicle.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a coolant activated drain plug.    Coolant activated drain plug (10)    Soluble plug (15)    Cavity (20)    Carrier (25)    Lines (40, 45)    Impedance element (50)