Here is a simple and effective way to monitor plus manage a battery. This combination of software and hardware I have used to manage my home solar battery bank. Undervoltage disconnect and load reconnect is implemented without any nuisance fast toggling at the setpoint.
Step 1: The Hardware.
I used a Labjack U3 to acquire a voltage signal from the battery bank. The U3 HV version can safely monitor up to 14VDC but for higher voltages like my 25.6VDC battery bank, I used a potentiometer. Of course, fuse or low current circuit breaker protection is recommended for this monitoring signal.
A windows PC is needed to support the Labjack U3 plus the necessary software. The more energy efficient, the better.
To get output signals to drive a relay or contactor for disconnecting the battery from load, a relay card is needed. Digital outputs from the Labjack are wired to the inputs of the relay card. Once an input is tied to 0VDC, its relay will activate.
Step 2: The Software.
The aim for a battery manager is to disconnect below a voltage low threshold and reconnect above a voltage high threshold. Also, a deadband is needed between both thresholds to prevent fast toggling or contactor buzzing. For example with my home, the reconnect is 25.0V and the disconnect is 23.5V.
I have put a screenshot plus the schematic file for the battery manager.
This same technique can be used for any variable, for example temperature, pressure, light etc. Any process monitoring that needs upper and lower thresholds with a deadband.
I hope for you flowstone users, this has been helpful.