Auto cut off 3.7 volt battery charger circuit - YouTube
10pcs 3.7V 4.2V Lithium Li ion 18650 Battery Charger Board DC DC Step Up Boost Lithium Battery Charging Step Up Board Module|Integrated Circuits| - AliExpress
3.7V Li-ion Battery Charger/USB Boost Power Module
Amazon.com: 18650 Battery Charger 4 Bay Smart Universal Charger for 3.7V Rechargeable Lithium Li ion Batteries Compatible 18650 26650 21700 10400 14500 16340 16650 18500 Battery Charger (Only AC Charger) : Electronics