Aircraft batteries and energy storage

This category covers aircraft main and emergency batteries, battery chargers and monitoring units, and the larger energy storage packs that electric and hybrid aircraft carry. The generator that charges the battery is under electrical power, and the motor that drains it is under electric propulsion. Chemistry is the reason this category behaves differently from every other box on the aircraft.

The approval, and the chemistry that follows it

Where a battery is approved as an article, a technical standard order authorisation is the FAA's design and production approval to a manufacturer that has shown the article meets the standard.¹ The same limit applies as everywhere else: that authorisation is not an approval to install and use the article on an aircraft.² Ask which standard the unit was qualified to, and ask specifically what the thermal runaway containment case is: what the cell-level failure does to the pack, what the pack does to the compartment, and what evidence supports the answer. For a lithium installation, ask what venting, containment and detection the installation assumes, and ask to see the test report rather than the summary.

It is also a dangerous good

Lithium cells and batteries are regulated in transport, and the rule that governs them sets out classification, packaging, state of charge and documentation requirements for shipping.³ The FAA maintains public resources on lithium battery safety aimed at everyone in the supply chain.⁴ This matters commercially, not just legally. Ask who ships the batteries, under what packing instruction, and what a shipment costs when it must move quickly. Ask what the storage requirements are at your line station: state of charge, temperature, segregation and quantity limits. Ask what the disposal route is at end of life and what it costs, because a pack you cannot ship is a pack you cannot return.

The service life is the price

Ask for the capacity check interval, the deep-cycle or reconditioning requirement, and who is allowed to perform it. Ask what calendar life and cycle life the manufacturer publishes, and which of the two will end your unit's service first at your utilisation. Ask what the capacity retention curve looks like at the temperatures your aircraft actually sees. Ask for the price of the unit, the price of a shop visit, and the price of the exchange pool, then build the cost per year. A cheaper battery with a shorter interval is usually the expensive one.

Where the public record can be checked

Airworthiness directives apply to appliances as well as aircraft, engines and propellers, and the FAA issues one when an unsafe condition exists and is likely to exist or develop in others of the same type design.⁵ Battery and charger directives are worth reading in full before a purchase: they show what failed, what the interim action was, and how long the terminating action took to arrive. The record proves the event and the required action. It does not tell you how many units were affected in service or how quickly the supplier shipped replacements, and both are fair questions to put to operators.

Questions that sort suppliers

Ask for the qualification report, including the thermal runaway testing. Ask for the shipping classification and packing instruction you will be working under. Ask for the published capacity check interval and the expected life in your operation. Ask what the return, exchange and disposal process is, with prices.