There are 3 primary methods of providing DC back-up power: buffer modules utilizing electrolytic capacitor arrays that provide milliseconds to seconds of back-up power, DC-UPS systems with built-in super capacitor arrays that provide seconds to minutes of back-up power, and DC-UPS systems with batteries that provide minutes to hours to days of back-up power. The period of back-up power is determined by the amount of power being backed up and the size of the capacitors or batteries utilized.