Understanding the charging voltages for lithium batteries is crucial for maintaining battery health and performance. This includes knowing the appropriate voltages for the bulk, absorption, and float stages of charging. For lithium batteries, the recommended voltage range for battery charging is between 14.2 and 14.6 volts.
Typically, lithium batteries require a constant current (CC) stage followed by a constant voltage (CV) stage for efficient charging.
Typically, you charge lithium batteries by applying the CC-CV scheme. CC-CV stands for Constant Current - Constant Voltage. It denotes a charging curve where the maximum allowed charging current is applied to the battery as long as the cell voltage is below its maximum value, for example, 4.2 Volts.
Lithium batteries have specific voltage requirements for charging, which can vary depending on the type of battery and its intended application. Tight voltage tolerances are necessary to ensure safe and efficient charging, preventing damage to the battery and extending its overall lifespan.
However (quoting you): charging at a constant voltage (say 4.2V) so long as the maximum current is limited to a reasonable value for the cell means you will have constant current charger till your cell is at ~95%. Up to this point the voltage across the battery will be less than 4.2V if you measure it.
Protection circuits built into the pack do not allow exceeding the set voltage. Figure 1 shows the voltage and current signature as lithium-ion passes through the stages for constant current and topping charge. Full charge is reached when the current decreases to between 3 and 5 percent of the Ah rating.