A system for an electric aircraft, the system comprising: • a battery pack onboard the electric aircraft; and • a circulation loop onboard the electric aircraft, the circulation loop comprising: • an onboard heat sink thermally coupled to the battery pack ; • an onboard circulation system comprising: • a distribution manifold fluidly connected to the onboard heat sink ; • a working fluid; • a pump connected to the distribution manifold and configured to continuously circulate the working fluid through the onboard heat sink during aircraft flight; wherein the onboard circulation system does not comprise an onboard compressor; characterized in that the system further comprises • a coupling configured to selectively connect the distribution manifold to an offboard cooling system , the offboard cooling system being configured to transfer heat from the working fluid to a sub-ambient cooling loop comprising an offboard compressor , • wherein the circulation loop and the battery pack are configured to cooperatively reject less than a threshold percentage of thermal energy generated by the battery pack during aircraft flight. • a battery pack onboard the electric aircraft; and • a circulation loop onboard the electric aircraft, the circulation loop comprising: • an onboard heat sink thermally coupled to the battery pack ; • an onboard circulation system comprising: • a distribution manifold fluidly connected to the onboard heat sink ; • a working fluid; • a pump connected to the distribution manifold and configured to continuously circulate the working fluid through the onboard heat sink during aircraft flight; wherein the onboard circulation system does not comprise an onboard compressor; characterized in that the system further comprises • a coupling configured to selectively connect the distribution manifold to an offboard cooling system , the offboard cooling system being configured to transfer heat from the working fluid to a sub-ambient cooling loop comprising an offboard compressor , • wherein the circulation loop and the battery pack are configured to cooperatively reject less than a threshold percentage of thermal energy generated by the battery pack during aircraft flight. • an onboard heat sink thermally coupled to the battery pack ; • an onboard circulation system comprising: • a distribution manifold fluidly connected to the onboard heat sink ; • a working fluid; • a pump connected to the distribution manifold and configured to continuously circulate the working fluid through the onboard heat sink during aircraft flight; wherein the onboard circulation system does not comprise an onboard compressor; characterized in that the system further comprises • a coupling configured to selectively connect the distribution manifold to an offboard cooling system , the offboard cooling system being configured to transfer heat from the working fluid to a sub-ambient cooling loop comprising an offboard compressor , • wherein the circulation loop and the battery pack are configured to cooperatively reject less than a threshold percentage of thermal energy generated by the battery pack during aircraft flight. • a distribution manifold fluidly connected to the onboard heat sink ; • a working fluid; • a pump connected to the distribution manifold and configured to continuously circulate the working fluid through the onboard heat sink during aircraft flight; wherein the onboard circulation system does not comprise an onboard compressor; characterized in that the system further comprises • a coupling configured to selectively connect the distribution manifold to an offboard cooling system , the offboard cooling system being configured to transfer heat from the working fluid to a sub-ambient cooling loop comprising an offboard compressor , • wherein the circulation loop and the battery pack are configured to cooperatively reject less than a threshold percentage of thermal energy generated by the battery pack during aircraft flight. <EOS>