Abstract: Certain embodiments are directed to components, subassemblies, systems, and/or methods for auxiliary power units (APU). In one embodiment, the APU is provided with a control system having an automatic start process. The automatic start process enables operation of the APU within a preset range of battery voltage, time, temperature and other parameters. In yet other embodiments, the APU is provided with a control system having a data verification process. The data verification process can be configured to set the operating mode of the APU. In one embodiment, the operating mode of the APU is a “purchase” mode. In other embodiments, the operating mode of the APU is a “lease” mode.