An interesting item appeared on eBay, for a Low initial price. eBay Item Number: 194175927781 ESE ES-181U Modem Master Clock https://www.ese-web.com/181.htm It has an internal gel cell battery (likely 6 Volt), and likely a Lithium Coin Cell for configuration settings. Designed to call USNO, or other Time Reference via POTS. At worst, a great Rack case with display. greg w9gb