Battery backups can also sometimes be called an uninterruptible power supply, uninterruptible power source, online UPS, standby UPS, and UPS. However, these units are named they all perform the same function. They are used to power the computer in case of electricity loss, as well some units also prevent damage to the computer from sudden increases in power or a slight drop. Often the surge protecting units will prevent damage to the attached components that are caused by lightning.
Battery backups can also be used to shut down or hibernate the computer safely when power fails. This prevents data loss from an unexpected shutdown. Some even run specialized software that when the backup is connected to the computer (often via a USB port), that will allow you to control the properties of the UPS such as how long to provide power to the computer before shutting it down, as well as using an audible alarm or not. This software can also provide information such as power loss details, current battery charge level, and charging status.
Often these devices have replaceable batteries, so they can be used for longer periods of time without replacing the entire unit. Some older units also offer surge protection for other items such as phone lines or the old-fashioned coax cable connector for televisions.
Battery backups vary in the amount of power they can supply and for how long. Many manufacturers offer tools on their websites to help you calculate which one to use. They also can have different numbers of plugs, including some units where some of the plugs have a backup, and others have only surge protection.
They come in a variety of sizes and shapes depending on their application. The simplest is similar to an oversized power bar. There are also mini-tower styles as well as highly sophisticated rackmount versions for use in server environments. The min-tower and rackmount units often have a display that shows the current status of the device and power.
For home and work-from-home computing, a UPS is useful to get past inconvenient power loss, but for businesses, they are often essential.