This read-only display string reports the state of the Memory Backup Battery Low alarm for the Ps1 controller, sourced from the BBL1 alarm point. It flags that the small internal battery that preserves the controller's memory or clock during a power loss is running low, distinct from the main plant battery strings. For example, an admin seeing this alarm active would schedule replacement of the controller's internal backup battery to avoid losing configuration or clock settings during a future outage.