One of the most common components in both the utility and industrial/commercial power system is the stationary battery. In many cases, the original design is marginal or inadequate; the maintenance and testing is practically nonexistent; but the system is called upon during emergency conditions and is expected to perform flawlessly. This paper begins with basic battery theory starting with the electrochemical cell. A working knowledge of the battery cell is important to understand typical problems such as hydrogen production, sulfating, and battery charging. The paper then discusses some of the common batteries and battery chargers. While this paper concentrates primarily on the lead acid type of battery, the theory can be utilized on other types such as the nickel-cadmium. Reference is made to industry standards and codes which are used for the design, installation, and maintenance of battery systems. Along with these standards is a discussion of the design considerations, maintenance and testing, and, finally, some advanced battery system topics such as individual battery cell voltage equalizers and battery pulsing units. The goal of this paper is to provide the reader with a basic working understanding of a battery system. Only with that knowledge can a person be expected to design and/or properly maintain a battery system which may be called upon during an emergency to minimize the effects of a normal power outage, to minimize personnel hazards and to reduce property damage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>