Keeping the Lights On: Aircraft Batteries
All but the most rudimentary aircraft require batteries to run their various electrical systems, such as lighting, avionics, communications equipment, and more. Batteries are mostly used in the preflight sequence before takeoff, to power the aircraft’s electrical system and start the engines and auxiliary power unit (APU). Once the aircraft is in flight, the APU will typically take over powering electrical circuits as well as recharge the batteries for the adapter emergency lighting for flight.
Batteries universally consist of several components:
- A voltaic cell: An electrochemical cell that derives chemical energy from spontaneous redox (reduction-oxidation) reactions taking place within the cell.
- An anode: A positive electrode in the voltaic cell, the electrode at which oxidation reactions take place resulting in a loss of electrons.
- A cathode: a negative electrode in a voltaic cell, at which reduction reactions take place resulting in a gain of electrons.
- Electrolytes: chemical compounds that, when fused or dissolved in certain solvents such as water, conduct electric current. Electrolytes in a fused state or solution produce ions which conduct electrical currents.
Batteries consist of one or more voltaic cells connected in series. Each cell contains one anode and one cathode, and a conductive electrolyte solution between them. When electrodes are connected to the electrolyte, a chemical reaction called reduction-oxidation, or redox, occurs. This electromotive force within the cell produces the electrical charge used to power devices connected to the battery.
Batteries used in aviation applications are either single-use or rechargeable. Aviation batteries must have a high energy density, be lightweight and reliable, require little maintenance, and be capable of operating over a wide range of environmental conditions. Common battery types include:
- Lead Acid: Consisting of a lead oxide anode, a lead cathode, and an electrolyte solution of sulfuric acid, these batteries have good energy storage, but are heavy and have low energy density. Lead acid batteries are often used as the main batteries in an aircraft.
- Nickel Cadmium: These batteries feature an anode of cadmium hydroxide, a cathode of nickel hydroxide, and an electrolyte solution of potassium, sodium, and lithium hydroxides. Nickel cadmium batteries are low-maintenance, reliable, and capable of operating in a wide range of temperatures.
- Nickel-Metal Hydride: Featuring an anode of metal alloys capable of absorbing and releasing hydrogen, a cathode of nickel hydroxide, and an electrolyte solution of lithium, sodium, and potassium hydroxides, nickel-metal hydride batteries are small-capacity and maintenance free. They require precise charge-level monitoring to control gaseous exchanges and minimize heating, and in aviation are mostly used to power emergency systems such as doors and floor escape path lighting.
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