Lithium battery monitoring device from 1-8cans. Equipped with a special undervoltage alarm. It is possible to set the sound signal when the voltage is from 2.7 to 3.7 V. The setting step is 0.1 V.
From the reviews: "I ordered 4 pieces, all workers.I'll tell you a little life hack why I need so many testers: I am engaged in aircraft modeling and I have many planes. In order not to spoil the batteries from airplanes, and not to squander them, the airplane must be planted on time. I set this tester to 3.3V and now when I have 3.3V left on some bank, the tester starts beeping loudly, you can hear it even from 100 meters !!!! And in order not to rearrange the same tester from plane to plane, I attach my own tester to each plane and extend it with a wire to the battery compartment. It is very convenient, I recommend it to everyone "