... ±2%VACFrequencySynchronous with Input Frequency(Utility Mode)/50±0.2%Hz(AC Frequency exceed 46~54Hz)50 ... AudibleAlarmBattery DischargeBeeping sound every 4 seconds after utility power failsBeeping sound every second if battery approaches ... ≥90%IndicatorsLCDVFD/LCD Indicator StatusInput/Output Voltage,Frequency,Output Power,Battery,Utility,Inverter,Overload,Fault,BypassCommunication PortRs232/ ...