Here is a very useful project of low battery voltage cutoff or disconnect circuit. Rechargeable batteries deliver very good performance and life if we take care of them. There are many things which can be done to take proper care and protect your rechargeable batteries which are not over charge
them, don't charge them in fast mode, don't get them fully discharge. When the batteries get fully discharge frequently then their life will get shorten and become dead in few weeks. Therefore it is better to disconnect your battery from the load when your battery become weak or require recharging. But it is very difficult to check and disconnect from the load every time they require charging. But the circuit shown here will do this job very efficiently by automatically monitoring the voltage of the battery and disconnect the battery from the load on the preset low voltage level of the battery.
The circuit is very simple to build and using few components. The heart of the circuit is a TL071 operational amplifier IC that is connected in comparator mode here. The 10K variable resistor is used to adjust the desired voltage level on which you want to deactivate the relay or disconnect the load from the battery. A 2N3904 transistor is connected at the output of the IC to drive the relay. The 5.1V zener is used as a voltage reference.
The circuit can be used with any type of batteries for example 12V, 9V, 6V, 5V etc. Only you have to change the 5.1V zener diode value according to the battery voltage type. For example if you want to use the circuit with 6V battery then simply change the zener diode value to 3.1V.