OT: Just about all the stuff you need inside the plane... switches, hoses, meters, cabling, etc. I cater to the big bird crowd.. aircraft that weigh more than 10 pounds. A big piece of the battery business I do is outside the 'hobby'.. I supply DARPA, Nasa-Langley, NRL and a few other 'beltway buyers' with cells and packs for original engineering and development projects.