10.3.2 Cell Construction
Lead-acid cells are composed of alternating positive and negative plates, interleaved with single or multiple
layers of separator material. Plates are made by pasting active material onto a grid structure made of lead
or lead alloy. The electrolyte is a mixture of sulfuric acid and water. In flooded cells, the separator material
is porous rubber, cellulose fiber, or microporous plastic. In recombinant cells with starved electrolyte
technology, a glass fiber mat separator is used, sometimes with an added layer of microporous polypropylene. Gell cells, the other type of recombinant cell, are made by absorbing the electrolyte with silica
gel that is layered between the electrodes and separators.
10.3.3 Battery Construction
Lead-acid aircraft batteries are constructed using injection-molded, plastic monoblocs that contain a
group of cells connected in series. Monoblocs typically are made of polypropylene, but ABS is used by
at least one manufacturer. Normally, the monobloc serves as the battery case, similar to a conventional
automotive battery. For more robust designs, monoblocs are assembled into a separate outer container
made of steel, aluminum, or fiberglass-reinforced epoxy. Cases usually incorporate an electrical receptacle
for connecting to the external circuit with a quick connect/disconnect plug. Two generic styles of receptacles
are common: the “Elcon style” and the “Cannon style.” The Elcon style is equivalent to military type
MS3509. The Cannon style has no military equivalent, but is produced by Cannon and other connector
manufacturers. Batteries sometimes incorporate thermostatically controlled heaters to improve low
temperature performance. The heater is powered by the aircraft’s AC or DC bus. Figure 10.1 shows an
assembly drawing of a typical lead-acid aircraft battery; this particular example does not incorporate a heater