A uninterruptible power supply or UPS for short, also known as a backup battery, is a device to ensure delivery of uninterruptible power to the connected equipment by supplying power from a separate source in case of mains power failure.
The vast majority of UPSs use VRLA lead accumulators.
There are several different types of UPS:
An off-line UPS is dormant until a power outage upon which it replaces the normal power supply with its own power source almost immediately. An on-line UPS, on the other hand, supplies constant power to the connected equipment from its reserves, while the reserves are recharged via the normal power supply. An on-line UPS is thus better protected against all typical power problems. An UPS is often used in the IT industry to secure, for example, computers (in server rooms) or telecommunications equipment during an unannounced power outage that could result in data loss or serious interference in a company. UPSs come in different sizes, where the largest usually co-operate with generators.