Buffer Battery

a storage battery connected in parallel with a DC generator or rectifying apparatus to supply a load jointly. It is called a buffer battery by analogy with a mechanical buffer—that is, it was originally intended to make up part of the power delivered by an electric generating set during periods of maximum load. It is frequently used as a reserve (in a mode of continuous floating operation with constant charging) in case the main supply sources fail (for example, in communications equipment). The storage batteries used in automobile and railway transportation also operate as buffer batteries: when the speed falls below a certain limit the generator is automatically disconnected, and the battery supplies the load independently.