Battery Charger
LM393 LITHIUM ION BATTERIES WITH LM317 FOR FAST CHARGING SCHEMATIC CIRCUIT DIAGRAM
Lithium-ion rechargeable battery Charge the battery at a voltage level of 1.5V per cell. of 4.2V or 4.1V or more when the stop
Regulations limit the supply voltage with a constant voltage + LM317 current cap of + LM393 to detect and stop the current termination charge is a simple enough. And probably not fully charged.