NOVELTY - A perforation tool (200) comprises an engaging tip (235) configured to mechanically breach a thermal-control-agent-retaining enclosure (205) of a traction battery pack including interconnected batteries with the enclosure reinforced for mechanical protection of the batteries when installed in an electric vehicle (230); a port (245) for receiving a thermal-control agent having a pressure of 5-100 psi; and a housing, coupled to the tip and to the port, where the tip includes an aperture, and where the housing includes a channel (250) communicating port to aperture.    USE - In battery enclosure system for making a vehicle battery pack (claimed).    ADVANTAGE - The perforation tool provides coolant agent ingress of a high energy density battery enclosure during an internal thermal event for situations in which a special fill port is unavailable; and has ability to terminate/mitigate a runaway thermal condition inside a battery enclosure for a high energy battery pack, such as the type used in electric vehicles and similar applications.    DETAILED DESCRIPTION - A perforation tool (200) comprises an engaging tip (235) configured to mechanically breach a thermal-control-agent-retaining enclosure (205) of a traction battery pack including interconnected batteries with the enclosure reinforced for mechanical protection of the batteries when installed in an electric vehicle (230); a port (245) for receiving a thermal-control agent having a pressure of 5-100 psi; and a housing, coupled to the tip and to the port, where the tip includes an aperture, and where the housing includes a channel (250) communicating port to aperture, where the pressurized thermal-control agent is produced at the tip at about the pressure. INDEPENDENT CLAIMS are included for the following:    (1) a perforation-enabled battery enclosure system for a vehicle battery pack, either comprising a thermal-control-agent-retaining enclosure of a traction battery pack including interconnected batteries with enclosure reinforced for mechanical protection of batteries when installed in an electric vehicle, and a perforation region defined in a portion of a wall of enclosure, where the perforation region configured with a selectably mechanically weakened wall allowing controlled breaching that defines an inlet port permitting an ingress of a thermal-control agent into the enclosure through the inlet port; or an electric vehicle including a chassis and a body, a thermal-control-agent-retaining enclosure of a traction battery pack including interconnected batteries with the enclosure reinforced for mechanical protection of batteries when installed in electric vehicle, a perforation region defined in a portion of a wall of enclosure, and a perforation tool, where the tool includes a tip, a fill port, and a channel communicating the fill port to an aperture defined proximate the tip, the tip mechanically breaching the wall to define the inlet port, the tool engaging the enclosure to resist disengagement when the thermal-control agent is pumped into the enclosure through the perforation tool at a pressure of 5-100 psi;    (2) manufacturing the perforation-enabled battery enclosure system for a vehicle battery pack, involving enclosing the vehicle battery pack within a thermal-control-agent-retaining enclosure of a traction battery pack including interconnected batteries with enclosure reinforced for mechanical protection of batteries when installed in an electric vehicle, and enabling access to an interior of enclosure through a perforation port to be created post-manufacture in a portion of a wall of enclosure, where the portion of wall mechanically weakened where other portions of wall maintain increased structural integrity; and    (3) filling a perforation-enabled battery enclosure system for a vehicle battery pack with a thermal-control agent, involving perforating a thermal-control-agent-retaining enclosure of a traction battery pack including interconnected batteries with enclosure reinforced for mechanical protection of batteries when installed in an electric vehicle where the perforating step breaches a region of a wall of enclosure to produce a perforation port, and filling enclosure through perforation port formed in portion of wall of enclosure.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic block diagram of a perforation-enabled battery enclosure system for a vehicle battery pack.    Perforation tool (200)    Enclosure (205)    Vehicle (230)    Engaging tip (235)    Port (245)    Communication channel (250)