As told earlier when a battery pack is formed by placing the cells in series it is made sure that all the cells are in same voltage levels. So a fresh battery pack will always have balanced cells. But as the pack is put into use the cells get unbalanced due to the following reasons. SOC Imbalance
For example a slight increase in charging voltage from 4.2V to 4.25V will degrade the battery faster by 30%. So if cell balancing is not accurate even slight overcharging will reduce the battery life time. As the batteries in a pack get older few cells might be weaker than its neighboring cells.
Number of cells: The balancing system becomes more complex with the number of cells in the battery pack. Balancing method: Choose active and passive balancing techniques based on the application requirements. Balancing current: Determine the appropriate balancing current to achieve efficient equalization without compromising safety.
Without proper protection, may cause an excessive discharge of lead-acid batteries for early damage. Therefore, lead-acid battery module requires a simple balance circuit to improve battery life in order to avoid over-voltage or under-voltage condition occurs.
Failure to properly balance cells can result in reduced usable capacity, shortened battery life, and safety hazards. Here are some of the challenges associated with battery cell balancing and various cell imbalance factors are shown in Fig. 17. The causes and solutions of cell imbalance is presented in Table 12. Fig. 17. Cell imbalance factors.
Battery balancing cannot fix a completely dead or damaged cell. Balancing equalizes charge levels among functional cells. If a cell is severely degraded or has failed, you may need to replace it to restore the battery pack’s performance.