Aircraft batteries provide stored electrical energy for times when engines or generators are not available. They can power essential instruments, radios, emergency lighting, and control electronics during startup or an electrical failure. Batteries also help start the auxiliary power unit, or APU, which can then supply electrical power and compressed air for engine start.
In aviation, battery reliability matters because backup power can protect the aircraft during critical phases of flight.
Key Facts
- Electrical energy stored in a battery can be estimated by E = VIt, where V is voltage, I is current, and t is time.
- Battery capacity is often rated in ampere-hours: capacity Ah = current A × time h.
- Power delivered to a load is P = VI, where P is power, V is voltage, and I is current.
- Nickel-cadmium batteries tolerate high discharge rates and cold conditions, but they need maintenance to control memory effect and electrolyte condition.
- Lithium aircraft batteries have high energy density and low weight, but they require a battery management system to monitor cells and prevent unsafe operation.
- Thermal runaway is a dangerous chain reaction in which battery heat causes more internal heating, so aircraft batteries use monitoring, containment, cooling, and isolation.
Vocabulary
- Auxiliary Power Unit
- An auxiliary power unit is a small onboard engine that provides electrical power and compressed air when the main engines are not supplying them.
- Essential Bus
- An essential bus is an electrical distribution path that feeds the most important systems needed for safe flight and landing.
- Nickel-Cadmium Battery
- A nickel-cadmium battery is a rechargeable aircraft battery type known for strong current output, durability, and reliable cold-weather performance.
- Lithium Battery
- A lithium battery is a rechargeable battery type with high energy per unit mass that must be carefully monitored for voltage, temperature, and current.
- Battery Management System
- A battery management system is an electronic controller that monitors battery cells and protects them from overcharge, overdischarge, overheating, and imbalance.
Common Mistakes to Avoid
- Confusing battery capacity with power is wrong because ampere-hours describe how long a battery can supply current, while watts describe the rate of energy delivery.
- Assuming the battery powers the whole aircraft during an emergency is wrong because backup power is usually routed to essential systems only to preserve limited energy.
- Treating nickel-cadmium and lithium batteries as interchangeable is wrong because they need different chargers, monitoring methods, maintenance procedures, and safety protections.
- Ignoring battery temperature limits is wrong because overheating can reduce performance, damage cells, or trigger thermal runaway in severe cases.
Practice Questions
- 1 A 24 V aircraft battery supplies 20 A to essential loads for 30 minutes. How much energy does it deliver in watt-hours?
- 2 An APU starter draws 300 A from a 28 V battery for 12 seconds. What power is delivered during starting, and how much energy is used in watt-hours?
- 3 A lithium aircraft battery is lighter than a nickel-cadmium battery with similar usable energy, but it needs a battery management system and thermal protection. Explain why an aircraft designer might choose either battery type depending on the mission and safety requirements.