This is typically five to 20 minutes, depending on the application. After the batteries are depleted, the load will crash. Very often, companies are so concerned with electrical reliability that the mechanical plant is overlooked. Most critical systems require temperature control to maintain reliable operations. Some equipment may also be water-cooled which requires a reliable, if not uninterruptible power source.
Redundancy is equally important on the mechanical side.
Redundancy needs to be evaluated for the HVAC, refrigeration plant, air-handling system, fuel oil system, building automation system, and water service. Failure of any of these components can bring a facility to its knees. Maintenance is critical. Once you have invested a significant amount of money and time to protect your facility from failure, preventive maintenance becomes the key to protecting your investment. Preventive as well as predictive maintenance plays a critical role in the reliability of both the electrical and mechanical systems.