Title 14 of the Code of Federal Regulations (14 CFR) Part 25 sets the airworthiness standards for transport category aircraft in the United States. Section 25.1353 specifically addresses the installation of battery and battery charger equipment. Following lithium-ion battery incidents on the Boeing 787 in 2013, the FAA issued Special Conditions for lithium battery installations in transport aircraft.
As electric and hybrid-electric propulsion matures, 14 CFR Part 25 is being updated to address high-power traction battery systems. The companion European standard is EASA CS-25. For eVTOL aircraft certified under Part 23 (normal category), equivalent provisions apply via Special Conditions tailored to each programme.
References: 14 CFR § 25.1353 (eCFR)