Low temperature rechargeable batteries are important to life in cold climates, polar/deep‐sea expeditions, and space explorations. Here, this work reports 3.5–4 V rechargeable lithium/chlorine (Li/Cl2) batteries operating down to −80 °C, employing Li metal negative electrode, a novel carbon dioxide (CO2) activated porous carbon (KJCO2) as the positive electrode, and a high ionic conductivity (≈5–20 mS cm−1 from −80 °C to room‐temperature) electrolyte comprised of aluminum chloride (AlCl3), lithium chloride (LiCl), and lithium bis(fluorosulfonyl)imide (LiFSI) in low‐melting‐point (−104.5 °C) thionyl chloride (SOCl2). Between room‐temperature and −80 °C, the Li/Cl2 battery delivers up to ≈29 100–4500 mAh g−1 first discharge capacity (based on carbon mass) and a 1200–5000 mAh g−1 reversible capacity over up to 130 charge–discharge cycles. Mass spectrometry and X‐ray photoelectron spectroscopy probe Cl2 trapped in the porous carbon upon LiCl electro‐oxidation during charging. At −80 °C, Cl2/SCl2/S2Cl2 generated by electro‐oxidation in the charging step are trapped in porous KJCO2 carbon, allowing for reversible reduction to afford a high discharge voltage plateau near ≈4 V with up to ≈1000 mAh g−1 capacity for SCl2/S2Cl2 reduction and up to ≈4000 mAh g−1 capacity at ≈3.1 V plateau for Cl2 reduction. This work reports a −80 °C ≈4.0 V rechargeable lithium/chlorine battery with a 1200–5000 mAh g−1 reversible capacity over up to 130 cycles, employing the newly engineered porous carbon cathode and SOCl2‐based electrolyte. X‐ray spectroscopy and mass spectrometry reveal the highly reversible LiCl/Cl2 redox reactions and trapping mechanism of reactive species at −40 °C to −80 °C.