I've got a circuit that runs on a 6S Lipo battery that switches some solenoid valves, powers an MCU, and has some other sensors (like pressure transducers). At max a draw of 4A. The lowest discharge for the 6S Lipo is 18v, before it becomes damaged, so I need a low voltage protection circuit that cuts off at 19 or 20v.
I have looked through all types of designs including using a zener diode, a comparator (with smaller regulated voltage and a divider), and other unique designs. In my case, I have a small MCU that will also be monitoring voltage, so I was considering using a simple CMOS flip-flop (with FET) and have the MCU "flop it" off with a pulse if the voltage is too low. Is that crazy? Would the "hanging flip flop" burn too much current in the off state?

 

Try this Circuit .........
It will require the addition of a Zener-Diode to protect the FET-Gate when used with a ~25-Volt-Supply.
You may want to replace the suggested FET with one rated for at least twice your expected Current.
The "Off-Button" is optional, the "On" or "Reset-Button" is required.
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Oh interesting... I had not seen that Shunt Voltage Regulator. I will play around with one of these. Thanks @LowQCab