The charge voltage limit refers to the maximum amount of voltage that can be applied during the charging process without causing damage to the battery. By knowing and adhering to this limit, you can prevent overcharging or undercharging, both of which can negatively impact battery health.
The ideal voltage for a lithium-ion battery depends on its state of charge and specific chemistry. For a typical lithium-ion cell, the ideal voltage when fully charged is about 4.2V. During use, the ideal operating voltage is usually between 3.6V and 3.7V. What voltage is 50% for a lithium battery?
Different types of batteries have different charge voltage limits. Another factor to consider is the temperature at which the battery is being charged. Extreme temperatures, whether hot or cold, can affect the battery’s ability to accept a full charge and may require adjustments to the charging voltage.
Nominal Voltage: This is the battery’s “advertised” voltage. For a single lithium-ion cell, it’s typically 3.6V or 3.7V. Open Circuit Voltage: This is the voltage when the battery isn’t connected to anything. It’s usually around 3.6V to 3.7V for a fully charged cell. Working Voltage: This is the actual voltage when the battery is in use.
For example, almost all lithium polymer batteries are 3.7V or 4.2V batteries. What this means is that the maximum voltage of the cell is 4.2v and that the "nominal" (average) voltage is 3.7V. As the battery is used, the voltage will drop lower and lower until the minimum which is around 3.0V.
To determine how much the battery voltage should be reduced to stay below the 5.7-V input voltage limit, consider the maximum battery voltage of 48-V. At this value, the voltage must be divided down by a factor of 8.42. For this example, we round up to 9 to be safe. Next, use the external hysteresis tool posted on this E2E thread.