The most suitable charging process for Li-ion batteries can be divided into four stages: trickle charging, constant current charging, constant voltage charging, and charge termination.

Phase 1: Trickle Charge Trickle charge is used to pre-charge (recovery charge) fully discharged cells first. When the lithium-ion battery voltage is lower than about 3V, the battery is first charged with a constant current of maximum 0.1C.

Stage 2: Constant current charging When the battery voltage rises above the trickle charging threshold, increase the charging current for constant current charging. The current for constant current charging is between 0.2C and 1.0C. The current during constant current charging is not required to be very precise, and a quasi-constant current can also be used. In linear charger designs, the current often rises with the battery voltage to minimize heat dissipation issues on the pass transistors.

Stage 3: Constant voltage charging When the lithium-ion battery voltage rises to 4.2V, the constant current charging ends and the constant voltage charging stage begins. For optimum performance, the regulation tolerance should be better than +1%.

Stage 4: Charge Termination Unlike nickel batteries, continuous trickle charging of Li-ion batteries is not recommended. Continued trickle charging can lead to a plate-plating effect on lithium metal. This can make the battery unstable and potentially lead to a sudden automatic rapid disintegration.