This is very easy 3.7 Volt Battery Charger Circuit to indicate the battery is full or empty and… | Battery charger circuit, Lithium battery charger, Battery charger
USB 3.7V Li-Ion Battery Charger Circuit - Homemade Circuit Projects
3.7V Lithium Battery Charger Protection Board 5V 1A 2A Li ion Lipo Battery Charging Protect Two in one Module Micro USB Type C|module 5v|module boardmodule charger - AliExpress
LTC1733: Thermal Regulation Maximizes Lithium-Ion Battery Charging Rate Without Risk of Overheating | Analog Devices
Single Universal 3.7 V Li-Ion Battery Charger - Electrothinks
DIY 3.7V to 5V Boost Converter for Lithium-Ion Battery