The Complete Handbook of UPS Batteries

Chapter 1: Understanding UPS Batteries

A UPS battery is the single most critical component in any uninterruptible power supply, and the one most likely to fail. The rest of the UPS - the charger, the inverter, the static switch - is solid-state electronics that can run for decades. The battery is an electrochemical device with a finite life, a discharge-and-recharge cycle that slowly degrades it, and a failure mode that is not always predictable. Yet most UPS documentation treats the battery as a sealed black box: install it, let it float, replace it when the alarm sounds. That approach costs businesses real money in the form of premature replacements, unexpected outages, and downtime that a properly maintained battery would have prevented.

To understand what a UPS battery actually is, you need to separate it from the battery in your car or your drill. A UPS battery is a storage device that is kept at full charge, at a constant voltage, by a charger that is always running. It is not deep-cycled the way a forklift battery is, but it can be called upon to deliver a large amount of current at a critical moment, sometimes for just a few minutes, sometimes for a full hour or more. The vast majority of UPS systems sold today - from a 500 VA unit under an office desk to a 500 kVA unit in a data center - use valve-regulated lead-acid (VRLA) batteries. You will also encounter flooded lead-acid batteries in larger, older