An electronic price display system uses an RF communications channel between a central computer and a multiplicity of electronic price display labels. Each label is powered by a voltaic cell ("battery") such as a lithium cell. The receiver-on time, which in other RF-linked systems contributes heavily...http://www.google.de/patents/US6130603?utm_source=gb-gplus-sharePatent US6130603 - Low-powered RF-linked price display system
