A UPS battery, or uninterruptible power supply battery, is a type of continual power system that provides automated backup electric power to a load when the input power source or mains power fails. It is not the same as a battery backup, as it responds instantly to power failure. The UPS battery system is designed to provide a big boost of power to the system and then hand things off to the backup system as soon as it is up and running. The on-battery run-times of most UPSs are relatively short, only a few minutes, but sufficient to "buy time" for initiating a standby power source or properly shutting down the protected equipment.

There are three main types of UPS batteries: Valve Regulated Lead Acid (VRLA), Flooded Cell or VLA batteries, and Lithium Ion batteries. The run-time for a battery-operated UPS depends on the type and size of batteries and rate of discharge, and the efficiency of the inverter. The total capacity of a lead–acid battery is a function of the rate at which it is discharged. Multi-kilowatt commercial UPS systems with large and easily accessible battery banks are capable of isolating and testing individual cells within a battery string.

Its important to understand that all UPS systems are not created equal. Rather, there are three primary topologies: standby, line-interactive, and online. Each type of UPS topology not only delivers varying levels of protection against power problems but achieves the result in a separate manner while placing differing frequency demands on the battery.