This rulemaking amends the Hazardous Materials Regulations (HMR) to (1) prohibit the transport of lithium ion cells and batteries as cargo on passenger aircraft; (2) require all lithium ion cells and batteries to be shipped at not more than a 30 percent state of charge on cargo-only aircraft; and (3) limit the use of alternative provisions for small lithium cell or battery to one package per consignment. The amendments do not restrict passengers or crew members from bringing personal items or electronic devices containing lithium cells or batteries aboard aircraft, or restrict the air transport of lithium ion cells or batteries when packed with or contained in equipment. To accommodate persons in areas potentially not serviced daily by cargo aircraft, PHMSA provides a limited exception for not more than two replacement lithium cells or batteries specifically used for medical devices to be transported by passenger aircraft and at a state of charge greater than 30 percent, under certain conditions and as approved by the Associate Administrator. This rulemaking is necessary to meet the FAA Reauthorization Act of 2018, address a safety hazard, and harmonize the HMR with emergency amendments to the 2015-2016 edition of the International Civil Aviation Organization's Technical Instructions for the Safe Transport of Dangerous Goods by Air.