These back-up combination sump pump systems come with a battery-powered, back-up pump and often include a back-up pump and a primary pump all contained in one unit. Systems automatically sound an alarm and activate a back-up sump pump when the primary sump pump malfunctions or when the main electrical power supply fails. In an emergency these systems can provide enough time to either replace the malfunctioning primary pump or for the electric power to be restored. They include a back-up sump pump, controller, battery case, and often a primary sump pump.