Ok, I see the AC Neg line sailing through and there is not separation from Line Voltage unless I put the device on the Battery power side, If on the Surg side I will be susceptible to brown out. It's like a backup generator system, once Voltage stops it kills power, and begins generating. But, with a UPS it requires a reset.
But, nothing is said as to how low line voltage drops for it to kicks out and will not try buck boost the voltage.
Still a bit confused.