AC 20-184A
2.4.1.2 If the FAA requires ground and/or flight tests, pe r the compliance checklist in the certification plan, then the applicant should perform the tests to demonstrate the lithium battery systems and the systems in which they are installed will not have any adverse effect on the aircraft.
2.4.1.3 If the FAA requires Electromagnetic Interference/Radio Frequency Interference (EMI/RFI) test, pe r the compliance checklist in the certification plan, then the applicant should perform the electromagnetic compatibility test described in AC 20-190, Aircraft Electromagnetic Compatibility Certification, to determine that the installation of the lithium battery does not have any adverse effect on aircraft systems and that the aircraft systems do not have any adverse effect on the lithium battery. This will demonstrate that the battery system functions as designed during normal aircraft operations.
2.5 System Safety Assessment.
The safety assessment of the lithium battery installation should address the battery system, the aircraft interface, and the aircraft functional loads to which the battery system provides power.
2.5.1 Perform a system safety assessment to show compliance with §§ 25.1309, 27.1309,
29.1309 a nd 23.2510 a nd all applicable SCs with respect to lithium batteries. This assessment should address concerns associated with the installation of the lithium batteries and battery systems, the possibility of direct (or indirect) injury to a person, any adverse effect on crew function, or any adverse effect on other equipment and systems. These effects could be a result of normal operation or a failure in the lithium batteries. Y our safety system assessment should consider, but not be limited to, the following:
• The levels of hazard associated with installation and use of lithium batteries.
• Whether design assurance level of lithium batteries is appropriate for performance and safety requirements based on location and intended function.
• No interference due to any failures of the lithium batteries.
• System separation and zonal analysis.
• Impact on flightcrew for normal and non-normal operation.
• Impact of emergency procedure during egress.
• Protection against fire, smoke, and electrical shock hazards.
• Other safety analysis appropriate to the system being installed.
• Statement of compliance for each requirement (SCs or SOs, as appropriate).
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2.5.2 Coordinate your assessment with the responsible certification branch to determine the depth of analysis required. Include a system description, a description of how the system is installed on the aircraft, and a list of functions and criticality.
2.6 Software.
To ensure intended function and safe operation of the software when showing compliance with §§ 25.1301, 27.1301, 29.1301, 25.1309, 27.1309, 29.1309, 23.2505,
23.2510 a nd all other applicable regulations, all lithium batteries that use software should c omply with RTCA DO-178C, Software Considerations in Airborne Systems and Equipment Certification, or equivalent, for the appropriate design assurance level.
You can find additional guidance in the following ACs referenced in appendix A:
• AC 20-115D, Airborne Software Development Assurance Using EUROCAE ED- 12() and RTCA DO-178();
• AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes;
• AC 25.1309-1B, System Design and Analysis;
• AC 27-1B, Certification of Normal Category Rotorcraft; and
• AC 29-2C, Certification of Transport Category Rotorcraft.
2.7 Complex Electronic Hardware.
All lithium battery hardware that contains complex electronic hardware should c omply with the most recent revision of RTCA DO-254(), Design Assurance Guidance for Airborne Electronic Hardware, or AC 20-152A, Development Assurance for Airborne Electronic Hardware for compliance with §§ 2 3.1353, 23.2525, 25.1353, 27.1353, and
29.1353.
2.8 State of Charge.
Lithium batteries not maintained at an adequate state of charge degrade at a significantly higher rate. Additionally, overcharging of individual cells could lead to thermal runaway.
2.9 Flammability.
2.9.1 Unlike nickel-cadmium and lead-acid cells, rechargeable lithium batteries use electrolytes and other materials that are flammable. This material can serve as a source of fuel for an external fire if a cell failure occurs. Lithium batteries have the potential to ignite spontaneously or experience thermal runaway, which involves an uncontrolled temperature and pressure increase, resulting in propagation to adjacent cells.
2.9.2 Pursuant to §§ 23.2325, 23.2330, 25.853, 27.853, 29.853, 25.863, 27.863, 29.863, a nd
25.869, aircraft battery equipment must meet the flammability requirements that ensure 2-7
AC 20-184A
the protection of structure and critical systems. Test the materials to ensure they meet applicable certification requirements.
2.9.3 The DOT/FAA/AR-00/12, Aircraft Materials Fire Test Handbook, Chapters 1 through 10 and Chapter 15 describe an acceptable method of compliance with Part 25, a ppendix F. If thermal and acoustic insulation material is used as part of the battery equipment and exposed, the requirements of § 2 5.856(a), a ppendix F , part VI, at amendment 25- 111 (or later amendment) must be met. Refer to the test methods described by AC
25.856-1, Thermal/Acoustic Insulation Flame Propagation Test Method Details.
2.10 Instructions for Continued Airworthiness.
During the certification process of the lithium batteries (battery and/or installation), complete the ICA in accordance with the following:
• Section 21.50(b);
• Sections 23.1529, 25.1529, 27.1529, 29.1529;
• Section 25.1729;
• Part 23 appendix A ;
• Part 27 appendix A;
• Part 29 appendix A;
• Part 25 appendix H ; and
• FAA Order 8110.54A, Instructions for Continued Airworthiness, Responsibilities, Requirements, and Contents (or most recent revision).
2.10.1 Develop the ICA so it is compatible with other maintenance instructions for the aircraft.
2.10.2 Refer to Chapter 3 of this AC for additional details specific to the maintenance of lithium batteries on aircraft.
2.10.3 The ICA, in accordance with the applicable regulations referenced in paragraph 2.10, must contain an “Airworthiness Limitations” section. Pursuant to §§ 43.1 6 and 91.403, the “Airworthiness Limitations” section is FAA-approved and specifies maintenance requirements, unless the FAA has approved an alternative program.
2.10.4 When a lithium battery installation is proposed, the ICA should also include at least the following information:
• Specifics of the lithium battery installation, including individual component part numbers and any other unique installation requirements,
• Electrical wiring diagrams/schematics, electrical equipment drawings,
• Maintenance instructions, basic control and operation, testing, servicing, maintenance schedule, inspection, troubleshooting, removing parts, replacing parts, 2-8
AC 20-184A repairs, special tools, fixtures, e quipment, and component manual information when appropriate (reference p aragraph 3.10.6), a nd
• Configuration control and storage instructions.
2.11 ICA Recommended Manufacturer’s Maintenance and Inspection Requirements.
The ICA, in accordance with the applicable regulations referenced in paragraph 2.10, must contain the recommended manufacturer’s maintenance and inspection requirements to ensure batteries whose function is required for safe operation of the aircraft will perform their intended function when installed. The ICA must contain:
2.11.1 Operating instructions and equipment lim itations in an installation manual (Type Certification) or a supplemental installation maintenance manual (Supplemental Type Certification).
2.11.2 Installation procedures and limitations sufficient to ensure cells or batteries, when installed according to the installation procedures, still meet the airworthiness requirements of the aircraft. The limitations must identify any unique aspects of the installation.
2.11.3 Maintenance requirements for measurements of battery capacity at appropriate intervals to ensure the battery whose function is required for safe operation of the aircraft will perform its intended function when installed in the aircraft.
2.11.4 Scheduled servicing information to replace batteries at the manufacturer’s recommended replacement interval.
2.11.5 Maintenance and inspection requirements for a visual check of the battery and/or charger degradation.
2.11.6 The ICA should also contain maintenance procedures for lithium batteries in spares storage to prevent the replacement of batteries with batteries that have experienced degraded charge retention ability or other damage due to prolonged storage.
2.11.7 The ICA, in accordance with the applicable regulations referenced in paragraph 2.10, must contain instructions to replace batteries based on the original equipment manufacturer (OEM) maintenance manual. Replacement of individual cells within lithium batteries must be approved by the OEM and the FAA. Do not mix cells from different manufacturers within a lithium battery, unless an alternate means proposed by the OEM and approved by the FAA exists.
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AC 20-184A CHAPTER 3. MAINTENANCE AND OPERATIONAL CONSIDERATIONS FOR LITHIUM
BATTERY SYSTEMS
3.1 Introduction.
Lithium batteries can be hazardous if not maintained a nd handled properly. This chapter provides guidance for maintenance considerations for aircraft lithium b atteries.
Maintenance requirements are part of the ICA that must comply with § 21.50 and to the applicable 23.1529, 25.1529, 27.1529, 29.1529 sections. This AC has appendices that include further relevant references to assist in compliance (i.e. recording pertinent maintenance data to document the service life of the lithium battery and battery system to ensure the airworthiness of the battery system and aircraft).
3.2 Aircraft Battery Maintenance.
Manufacturer procedures for maintenance should be followed because maintenance and inspection requirements for aircraft lithium batteries vary based on the type of chemical technology and physical construction of the battery. Performance of lithium batteries at any time in a given installation will depend on several factors that include but are not limited to the following (refer to 14 CFR § 43.1 3 for additional requirements):
3.2.1 Lithium Battery Chemistry.
The electrolyte used in lithium batteries can be a highly reactive substance and care must be observed in maintaining the lithium batteries in accordance with both the OEM maintenance manual and the applicable regulations referenced in table 2-1.
3.2.2 Age Management.
To determine the life and age of the installed lithium battery, record the installation date of the battery. During normal battery maintenance, document battery age in either the aircraft maintenance log or the shop maintenance log. Do not keep batteries in service longer than recommended by the manufacturer.
3.2.3 State of Charge.
State of charge of the lithium battery is determined by the cumulative effect of charging and discharging the battery. In a normal electrical charging system, the generator or alternator restores a battery to full charge during a flight regardless of use before flight.
However, safeguards must be implemented to ensure the aircraft does not begin flight with a battery not sufficiently charged to accomplish its intended function of continued safe flight and landing of the aircraft in accordance with the applicable regulations referenced in table 2-1. (See appendix E , Note 1, for the definition of “sufficiently charged”.)
3.2.4 State of Health.
Determine the state of health of the lithium battery by r ecording various parameters including t he following:
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AC 20-184A
• Length of time the battery has been installed and in service.
• The state of charge of the battery. The output of this function may be used for dispatch or maintenance purposes.
3.2.5 Mechanical Integrity.
In accordance with the applicable regulations referenced in table 2-1, and to ensure proper mechanical integrity, the battery must be inspected to ensure it is free of any physical damage before use. Then the battery must be installed and connected properly.
The buildup of explosive gases can be avoided by incorporating positive battery venting for the battery and battery compartment systems. Check periodically to ensure the venting system is securely connected and oriented in accordance with the maintenance manual’s installation procedures. Follow the procedures approved for the specific aircraft and battery system to ensure the battery system is capable of delivering the specified performance. The venting system should account for specific installation requirements of the aircraft.
3.2.6 Reliability of Charging/Monitoring Systems.
Follow the manufacturer’s recommendation for maintenance inspections concerning the battery charging and monitoring systems.
3.2.7 Shop-Level Maintenance Procedures.
In accordance with the applicable regulations referenced in table 2-1, shop procedures must follow the manufacturer’s recommendations (refer to § 43.13 for additional requirements).
3.2.8 Aircraft Battery Inspection.
Evidence of impending battery failure can sometimes be detected by a general visual inspection. Manufacturer-recommended inspections should include the following actions:
• Inspect battery terminals and all other connections for evidence of corrosion, pitting, arcing, and burns. Clean as required.
• Inspect the battery for improper installation (loose terminal screws, battery terminal links, or connector).
• Inspect the battery mounting.
• Inspect for evidence of physical damage.
3.2.9 Prior to the installation on aircraft, batteries in a rotable stock (which are parts and components that are easily exchanged between product) must be functionally checked at the battery manufacturer’s recommended inspection intervals in accordance with the applicable regulations referenced in table 2-1. Some failure modes may include degraded charge retention capability or other damage due to prolonged storage.
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AC 20-184 A
3.3 A ircraft Battery Replacement.
3.3.1 Ensure replacement batteries are in airworthy condition. An airworthy battery is one that has been conformed, installed, and tested on the aircraft as required by the FAA accepted ICA. Refer to the battery manufacturer maintenance manuals for proper maintenance of lithium b atteries. Refer to the aircraft maintenance procedures for the replacement of lithium batteries.
3.3.2 The ICA should include the manufacturer’s requirements for the mandatory battery replacement schedule (airworthiness limitation section) and periodic maintenance.
3.3.3 The installation process for lithium batteries can vary significantly across different aircraft systems. Always consult the specific aircraft manuals for detailed instructions on how to properly remove and install batteries. This ensures adherence to safety and technical specifications unique to each aircraft model.
3.3.4 Always inspect for corrosion and moisture on battery interfaces when replacing batteries. Failure to do so can lead to serious issues. Corrosion disrupts electrical connectivity, diminishing power efficiency and risking system failures. Moisture increases the risk of short circuits, potentially causing power losses and fire hazards.
Ensure these inspections are part of your regular maintenance routine to maintain battery reliability and safeguard against potential safety risks.
3.3.5 The maintenance record should reflect all battery replacements. Record the expiration date of the battery.
3.3.6 The lithium batteries should be replaced with an approved battery for the specific aircraft application.
3.3.7 Deep discharge may result in a potential unsafe condition. Replace the battery based on the manufacturer’s recommendation.
3.4 Aircraft Battery Storage and Handling.
3.4.1 Following the manufacturer’s recommended storage procedures will permit users to achieve the best results from their batteries.
3.4.2 Storage requirements vary with the battery type. Record the date of charging and, if the battery is not used within the manufacturer’s recommended interval, service the battery per the manufacturer’s recommendation.
3.4.3 To maintain battery integrity, follow the manufacturer’s recommendation for charged batteries that are being held in “ready for service” areas.
3.4.4 Handling procedures and precautions vary with battery size and configuration. Follow the manufacturer’s recommendation to prevent mishandling of the battery.
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AC 20-184A
3.4.5 Follow the manufacturer’s recommended procedure to prevent electrostatic discharge during storage and handling.
3.4.6 For packaging and shipping, f ollow the manufacturer’s recommended procedures.
3.4.7 Check batteries before use for any leakage or deformity. Do not use the batteries if there is any evidence of leakage or deformity.
3.4.8 Aircraft vibration and/or contact oxidation can result in poor electrical connections.
Ensure proper connector maintenance procedures are followed.
3.4.9 Observe the following precautions when handling lithium batteries:
• Do not store lithium batteries with other hazardous or combustible materials.
• Do not heat or incinerate lithium batteries.
• Do not dispose of lithium batteries with other waste unless allowed by applicable regulations.
• Use special care in handling lithium batteries. Do not open, puncture, crush, disassemble, or subject batteries to physical abuse.
3.4.10 Lithium batteries can be a personal safety hazard due to the possibility of lethal shock and must be labeled to clearly indicate the hazard in accordance with the applicable regulations referenced in table 2-1.
3.4.11 Follow all manufacturer’s recommended safety precautions and procedures.
3.4.12 Material Safety Data Sheets must be enclosed with lithium batteries for shipping i n accordance with the applicable regulations referenced in table 2-1. A ppropriate information from the MSDS should also be incorporated into the Component Maintenance Manuals (CMMs) and Aircraft Maintenance Manuals (AMMs) as warnings and cautions, as appropriate.
3.4.13 Always wear protective clothing, including gloves and safety goggles, when handling and disposing of lithium batteries. Proper disposal procedures should be followed to avoid environmental hazards and comply with applicable environmental regulations.
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AC 20-184A Appendix A APPENDIX A. RELATED REGULATORY AND ADVISORY MATERIAL The following regulatory and advisory materials are related to this AC:
A.1 Regulations.
The following 14 CFR regulations are related to this AC. You can download the full text of these regulations from the Federal Register website at www.ecfr.gov.
• Part 21, Certification Procedures for Products and Articles.
• Part 23, Airworthiness Standards: Normal Category Airplanes.
• Part 25, Airworthiness Standards: Transport Category Airplanes.
• Part 27, Airworthiness Standards: Normal Category Rotorcraft.
• Part 29, Airworthiness Standards: Transport Category Rotorcraft.
• Part 43, Maintenance, Preventive Maintenance, Rebuilding, and Alteration.
• Part 145, Repair Station.
A.2 Advisory Circulars.
The following ACs are related to the guidance in this AC. The latest version of each AC referenced in this document is available on the FAA website at FAA Advisory Circulars and on the Dynamic Regulatory System.
• AC 20-115D, Airborne Software Development Assurance Using EUROCAE ED- 12() and RTCA DO-178(), dated July 21, 2017.
• AC 20-128A, Design Considerations for Minimizing Hazards caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor Failure, dated March 25, 1997.
• AC 20-135A, Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria, dated September 29, 2025.
• AC 20-136B, Aircraft Electrical and Electronic System Lightning Protection, dated September 7, 2011.
• AC 20-152A, Development Assurance for Airborne E lectronic Hardware, dated October 7, 2022.
• AC 20-158B, The Certification of Aircraft Electrical and Electronic Systems for Operation in the High-intensity Radiated Fields (HIRF) Environment, dated May 20, 2024.
• AC 20-190, Aircraft Electromagnetic Compatibility Certification, dated June 1, 2018.
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AC 20-184A Appendix A
• AC 2 1 -16G, RTCA Document DO-160 versions D, E, and F , “Environmental Conditions and Test Procedures for Airborne Equipment”, dated June 22, 2011.
• AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes, dated November 17, 2011.
• AC 23-17C, Systems and Equipment Guide for Certification of Part 23 Airplanes and Airships, dated November 17, 2011.
• AC 25-16, Electrical Fault and Fire Prevention and Protection, dated April 5, 1991.
• AC 25.856-1, Thermal/Acoustic Insulation Flame Propagation Test Method Details, dated June 24, 2005.
• AC 25.863-1, (Aviation Rulemaking Advisory Committee (ARAC) draft) Flammable Fluid Fire Protection, U nder Development.
• AC 25.1309-1B, System Design and Analysis, dated August 30, 2024.
• AC 25.1322-1, Flightcrew Alerting, dated December 13, 2010.
• AC 25.1581-1, Airplane Flight Manual, dated October 16, 2012.
• AC 25.1701-1, Certification of Electrical Wiring Interconnection Systems on Transport Category Airplanes, dated December 4, 2007.
• AC 27-1B, Certification of Normal Category Rotorcraft, dated June 23, 2023.
• AC 29-2C, Certification of Transport Category Rotorcraft, dated June 23, 2023.
• AC 43.13-1B, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, dated September 8, 1998.
• AC 43.13-2B, Acceptable Methods, Techniques, and Practices—Aircraft Alterations, dated March 3, 2008.
• AC 120-16G, Air Carrier Maintenance Programs, dated January 4, 2016.
• AC 120-42B, Extended Operations (ETOPS and Polar Operations), dated June 13, 2008.
A.3 Form.
The following FAA forms are available on the FAA forms website at https://www.faa.gov/forms/.
• FAA Form 337, Major Repair and Altercation (Airframe, Powerplant, Propeller, or Appliance), dated October 01, 2006.
• FAA Form 8130-3, Major Repair and Alteration (Airframe, Powerplant, Propeller, or Appliance), dated October 1, 2006.
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A.4 Handbooks.
The following handbooks are available on the Federal Aviation Administration Fire Safety website at https://www.fire.tc.faa.gov/Reports/reports.asp. You should refer to the latest version for guidance.
• DOT/FAA/AR-00/12, Aircraft Materials Fire Test Handbook, dated April 2000.
• DOT/FAA/AR-04/26, Flammability Assessment of Bulk-Packed, Non-rechargeable Lithium Primary Batteries in Transport Category Aircraft, dated June 2004.
A.5 Orders.
The following orders are available on the Dynamic Regulatory System. You should refer to the latest version for guidance.
• FAA Order 8110.4C, Type Certification, dated October 20, 2023.
• FAA Order 8110.42D, Parts Manufacturer Approval Procedures, dated October 27, 2023.
• FAA Order 8110.48A, How to Establish the Certification Basis for Changed Aeronautical Products, dated July 21, 2017.
• FAA Order 8110.52B, Type Validation and Post-type Validation Procedures, dated September 29, 2017.
• FAA Order 8110.54A, Instructions for Continued Airworthiness Responsibilities, Requirements, and Contents, dated October 23, 2010.
• TSO C179b, Rechargeable Lithium Batteries and Systems, dated March 23, 2018.
A.6 Industry Documents.
A.6.1 International Electrotechnical Commission (IEC).
IEC document IEC 62133, Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications - Part 2: Lithium systems, dated February 7, 2017, is related to the guidance in this AC. The document is available online at https://webstore.iec.ch/en/.
A.6.2 RTCA.
The following RTCA (formerly Radio Technical Commission for Aeronautics) documents are related to the guidance in this AC. Unless otherwise specified, use the latest FAA-accepted revision for guidance. If the document is revised after publication of this AC, you should verify that the FAA accepts the subsequent revision or update as an acceptable form of guidance. The documents can be ordered online at https://www.rtca.org.
• RTCA DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment, dated December 8, 2010.
AC 20-184A Appendix A A-3
AC 20-184A Appendix A
• RTCA DO-178 (), Software Considerations in Airborne Systems and Equipment Certification, dated December 13, 2011.
• RTCA DO-254 (), Design Assurance Guidance for Airborne Electronic Hardware, dated April 19, 2000.
• RTCA DO-311A, Minimum Operational Performance Standards for Rechargeable Lithium Battery (Systems), dated December 19, 2017.
A.6.3 Society of Automotive Engineers (SAE) International.
The following SAE Aerospace Recommended Practice (ARP) documents are related to the guidance in this AC. Unless otherwise specified, use the latest FAA-accepted revision for guidance. If the document is revised after publication of this AC, you should verify that the FAA accepts the subsequent revision or update as an acceptable form of guidance. The documents are available online at: https://www.sae.org.
• ARP4754A, Guidelines for Development of Civil Aircraft and Systems, dated December 20, 2010.
• ARP4761, Guidelines for Conducting the Safety Assessment Process on Civil Aircraft, Systems, and Equipment, dated December 1, 1996.
A.6.4 UL.
The following UL (formerly Underwriters Laboratories) documents are related to the guidance in this AC. The documents are available online at https://www.shopulstandards.com/. Refer to the latest version of the referenced document for guidance.
• UL 1642, Lithium Batteries, dated October 12, 2022.
• UL 2054, Household and Commercial Batteries, dated March 10, 2022.
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