A lithium battery’s full charge voltage rises as it is charged. For instance, when a lithium-ion battery is ultimately charged, the voltage may increase from its nominal value—roughly 3.7 volts for a single cell—to around 4.2 volts. On the other hand, when a battery discharges, the voltage drops as the gadget draws power from the battery.
The voltage output of the charger must meet the voltage requirements of the lithium battery pack to ensure safe and efficient charging. Using a charger with incorrect voltage output will result in overcharging or undercharging, which may damage the battery and shorten its life.
When the cells are assembled as a battery pack for an application, they must be charged using a constant current and constant voltage (CC-CV) method. Hence, a CC-CV charger is highly recommended for Lithium-ion batteries. The CC-CV method starts with constant charging while the battery pack’s voltage rises.
Lithium-ion batteries operate differently. They charge under a constant current and switch to a continuous voltage later in the charging cycle. The charging process reduces the current as the battery reaches its full capacity to prevent overcharging.
When the battery reaches its full charge cut-off voltage, constant voltage mode takes over, and there is a drop in the charging current. The charging current keeps coming down until it reaches below 0.05C. The battery reaches full charge voltage some time after the CV mode starts (as soon as one of the cells reaches its full charge voltage).
On the other hand, undercharging can cause irreversible capacity loss, negatively impacting battery performance and life. Discharging below the minimum voltage threshold of a lithium battery must be avoided to keep the battery healthy and ensure optimal functionality. Using a certified charger to charge lithium battery packs must be considered.