We have a S539 Intercom and the specification data says it operates at 12vdc/3A or 24vdc/1.5A. I am wondering if that means that it will run on any voltage between 12 and 24vdc, or if it's somehow designed to only work at 12 and 24 but not the voltages in between?

Also, in the event of a power outage, this would be run directly from a battery bank at 24vdc. Those batteries will run down eventually, which means that the voltage will drop. Is this intercom designed to shut itself off in the event of undervoltage?