Many years ago my first calculator used an LED display and a 9V battery. It stopped working when the battery voltage dropped to less than 7.5V but then the battery still had plenty of power remaining. I added a 100uF capacitor parallel to the battery then the calculator worked until the battery was 4V and the display was so dim I could barely see it. When the battery is low the display dims each time the calculator is used.
My 3V Chaser project still works when the two AA alkaline cells drop to a total of only 1.8V (0.9V each). It uses a 74HC4017 guaranteed to work at 2V but most still work with a lower voltage.