Battery replacement on a 2019 Ford Edge. What is this red plug for?

Battery replacement on a 2019 Ford Edge. What is this red plug for? MACTFORDEDGE on Facebook:   / mactfordedge   Due to factors beyond the control of MACTFORDEDGE, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. MACTFORDEDGE assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. MACTFORDEDGE recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of MACTFORDEDGE, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not MACTFORDEDGE. Music: Musician: Band of one ( Kevin Messner) Song: Wake up (revamped) Song: Track 15 Song: Track 14 Contact: https://www.facebook.com/BaNd-Of-OnE-...