Nice item. When tested on the bench power supply, it turns completely out with 13.5 Volts. So it is not so accurate as would be expected. At least, it provides an idea of the charge of the connected circuit. I have expected more.
Online store: AliExpress
US $1.18 |1S 4S Single 3.7V Lithium Battery Capacity Indicator Module 4.2V Blue Display Electric Vehicle Battery Power Tester Li ion-in Integrated Circuits from Electronic Components & Supplies on AliExpress - 11.11_Double 11_Singles' Day
0.77 USD