Constant Current Constant Voltage (CC-CV)

Constant current constant voltage (CC-CV) is a charging method where the charger first supplies a steady current, then holds a steady voltage while the current tapers off. Lithium-ion and lead-acid batteries both charge this way.

For lithium-ion, Battery University says the battery is at about 85% when the constant current stage ends, and full when the current falls to 3% to 5% of its Ah rating. For lead acid, the constant current stage reaches about 70% in 5 to 8 hours.

The constant voltage stage is why the last part of any charge is slow. The guide to the EV charging curve covers EVs, and the guide to lithium vs lead-acid charging compares the stages for 12 volt batteries.