Learning about aircraft batteries will make you wish you had stayed awake in high school chemistry. That’s because batteries are electrical devices driven by a chemical reaction.
Inside the hard case sit individual cells, each capable of producing two volts. A 12-volt battery, therefore, has six cells. Two plates of lead, one solid lead and the other lead oxide, interlace within the cell. Surrounding all of it is a mixture of water and sulfuric acid that acts as an electrolyte, carrying electricity to and from the plates.
As the battery is called upon for power, the positive charge of the lead dioxide plate passes its energy through the electrolyte to the lead plate. Eventually, both equalize to form lead sulfate. When the battery is recharged the opposite happens, as the lead sulfate converts back to transform the positive plate to lead oxide.
Aviation uses two primary types of batteries: the traditional lead-acid battery and the more modern “sealed” battery, formally called a valve-regulated lead acid battery. In aviation applications, it features a fiberglass mesh between the plates that contains the electrolyte. Typically it’s marketed as an AGM battery, which stands for absorbed gas mat. Sealed batteries don’t require as much maintenance as the traditional lead-acid battery, they don’t discharge as fast, and they typically don’t leak fluid into the battery box—which can cause corrosion.
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