Hi
That's bizarre, I was under the impression anything under 216 is considered a brown-out and there are no guarantees all hardware can handle it, thus the point of having a UPS.
There is no hard and fast rule that dictates what a brownout voltage is. Essentially a brownout just means a temporary dip in the voltage from what is the norm. Check your IT power supplies, I expect most if not all will be switch mode power supplies and work internationally, so 100-240 volts rating. If you want to argue anything under 216 volt is a brownout then that means all IT equipment running in countries with 110-120 volts (which have exactly the same power supplies just different pins) are all running in a constant brownout situation and so must be damaged very soon and fail, but clearly that isn't the case.
Most UPS's are designed purposely not to transfer over to battery power until somewhat lower or higher than the max and mins of the supply companies voltage specification, simply because it isn't necessary to maintain the AC voltage within that range with IT equipment (they can run down to at least 100 volts and still work fine), and this saves wear and tear on the battery and the circuitry by switching only when necessary.
You can get online UPS's that will essentially regenerate the AC voltage 24/7 and the output voltage never varies, however these are more expensive and less efficient, and overkill for consumer use.
What you need to understand is UPS's are designed to maintain the voltage in a range
required by the attached equipment to continue to operate, not to maintain the grids AC voltage specification. A UPS isn't feeding back into the national grid, it's feeding IT equipment and is designed for that purpose.
Also worth remembering that IT equipment doesn't work on 240 volts, it is usually 12 volts or considerably less, so receive far higher volts than they need, there is a huge buffer between what IT equipment needs to run and what they get fed, which is why AC adaptors can be rated for use as low as 100 volts, and in reality they will be designed to run with some tolerances on those ratings, so will work quite a bit below 100 volts even. A brown out down to say 80 volts wouldn't cause a problem for most IT equipment. We've probably all experienced a blip in the power supply where the lights have dimmed for a split second yet things like TVs and computers have carried on working without a hiccup, it is because they can run on lower voltages.
If you have a power cut does your IT equipment attached to your UPS continue working okay?
Regards
Phil