The Central Battery System (CBS) Is Defined As A System In Which The Whole Of The Energy Required For The Transmission And Signaled Is Drawn From The Exchange. No Batteries Or Hand Generators Are Used At The Telephone End And The Calls Are Automatically Signalled, By Means Of Lamps, On The Exchange Switchboard. Supervisory Lamps Indicate To The Operator When Callers Have Cleared Down. This System Achieves Substantial Savings And Good Quality Transmission By Means Of The Central Power Source. The Need For Local Power And Hand Generators Was Only Retained For Test Telephones, Large Pmbx’s, Certain Extension Plans And Some Private Circuits, Although Today None Of These Are Generally In Use.