Battery Indication When controller in Fault
When a controller is in fault , whether it will still indicate the battery status . In single or redundant configuration.
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Once Controller is Powered on, irrespective of Controller's state, the Battery indication LED should glow. The LED is controlled by Software battery Voltage test and the Software performs cyclic battery voltage level tests via a dedicated LED control input.
The Battery indication remains ON (Normally) when voltage level of your internal/external battery is above 3.1V. If the 'B' LED flashes or goes off, then your battery should be changed (Internal/external)
More detailed information can be found on your AC800M Controller Hardware Manual