Understanding Undervoltage in LTC2965 - 100V Micropower Single Voltage Monitor?
The "/24V UNDERVOLTAGE" output goes low when the 24V supply is undervoltage, in this particular case it is less than 18.2V or between 20V and 18.2V and on the way up from &lt; 18.2V. It's an open drain output so it can be pulled up to whatever logic level you like (5V in this case). 

The maximum INH level is 2.402V * 40 = 96.08V and INL should be less than that. To get that nominal setting you use the 40:1 range rather than the 10:1 range shown in the diagram. 

The 3V supply lockout built into the chip is not much of a concern since your battery will be far above that under reasonable conditions (assuming it's actually connected). What that means is that the output is not guaranteed to be low if the supply voltage  Vin is &lt; 3V. 

The absolute maximum voltage of the chip is 140V so you may wish to add some protection (eg. with a TVS). 

If the 96V level (and perhaps 90V level, up to you to pick a level) for switching is acceptable you can connect INH directly to REF and add two resistor to determine the hysteresis. If you set the hysteresis too small the device may switch back and forth excessively, so your design has to take that into account.