Ni-Cd battery deep discharge protection circuit

I have a LED lamp in my workshop which I supply from a recycled 12V 3Ah Ni-Cd battery. To protect the battery from a deep-discharge I built a simple circuit from what I found around. The circuit is built into the lamp and starts to beep when the supply voltage drops to 10V. The beep means that the battery has to be replaced.

The potentiometer PR has to be adjusted: Just set the desired voltage at which the circuit has to beep and then find a position of the PR at which the circuit starts to beep. The TL431 is a shunt voltage regulator and will pull down the pin 1 of the CD4093 when the voltage on its pin 1 is higher than 2.5V. One gate of the CD4093 forms an oscillator running at audible frequency. 3 unused gates have their inputs tied to GND. Piezzo is a of a passive type, it doesn't have built in generator.

The circuit has been built a piece of prototype PCB.