This guide is intended to assist users who select battery systems for uninterruptible power systems (UPS). The guide informs users of the characteristics of the various battery energy systems available so they can select the system best suited to their requirements. This guide does not place any restrictions on the rectifier or inverter components of the UPS. It does, however, describe how those components can relate to the selection of the battery system. This guide divides the available technologies into the following two main categories: a) Lead-acid batteries, which include both vented (ßooded) and valve-regulated (sealed) constructions b) Nickel-cadmium batteries For each category, both the technology and the design of the battery are described in order to facilitate user selection. The specific advantages for particular applications are also listed. Several battery designs are available to the UPS user. Each design has advantages and disadvantages, all of which should be considered when selecting a battery.