GitHub - sparkfun/Uh-Oh_Battery_Indicator: Kit that turns on an LED when voltage drops below a settable threshold. Available from SparkFun Electronics.
Lithium Li-ion 18650 Packs BMS Battery Capacity Level LED Indicator Panel Meter | eBay
Battery Style Digital Tube LED Battery Level Display Module 4-color 10-segment LED Bar for
3.7V Battery Low and Full Level Indicator Circuit : 9 Steps (with Pictures) - Instructables
Digital 12V/24V LED Battery Status Charge Indicator Monitor Meter Gauge | eBay
Make Your Own LED Battery Level Indicator : 4 Steps - Instructables
Make your own LED 18650 Battery Level Indicator - YouTube