Electrical power is required for non-line-powered voice services to work. This includes Digital Home Phone and Connected Voice. If there is a power outage, the services will not process calls, including those to Emergency 911.
With active batteries, the BBU will provide temporary power during an outage, allowing basic voice services to keep functioning, including the ability to dial 911. Please note that in the event of an outage that impacts the internet network as well, the BBU may not guarantee functionality.