Gill Electric was founded in 1920 and surprisingly enough the original factory still stands in California. The founder, Mr. Lawrence Gill was producing batteries for automobiles and when World War broke out he transitioned into manufacturing batteries for both military vehicles and aircraft. Gill made huge strides in the technology of dry charging batteries prior to adding electrolyte. They provide OEM batteries for Airtractor, Ayres, Cessna, Learjet, Piper, and many other aircraft.
In 1966 Teledyne acquired Gill and the two firms together engineered a number of ground breaking batteries that continue to power aircraft all across the world.