Car battery pack runtime

Despite the growing demand for larger battery cells, battery prices remain quite high, constituting the most expensive component in an EV or PHEV, with a typical price tag of around $10,000 for a battery that supports a range of a few hundred kilometers. The high cost can be mitigated by using lower-cost/refurbished battery cells, but such cells will also have greater capacity mismatches, which will reduce the available runtime or driving distance on a single charge. Even higher-cost, higher-quality battery cells will age and mismatch after repeated use. There are two ways to increase the capacity of a battery pack with mismatched cells: one is to use larger batteries from the beginning, which is not cost-effective; the other is to use active balancing, a new technology that can restore battery capacity in the battery pack and quickly increase power. Full series battery cells need balancing When each battery cell in the battery pack has the same state of charge (SoC), we say that the battery pack is balanced. SoC refers to the current remaining capacity of an individual battery relative to its maximum capacity as the battery is charged and discharged. For example, a 10Ah battery will automatically equalize the state of charge between parallel-connected battery cells over time as long as there is a conductive path between the battery cell terminals. It can also be argued that the state of charge of series-connected cells will vary over time for a variety of reasons. Temperature gradients across the pack, impedance, self-discharge rates, or differences in load between individual cells can cause gradual changes in SoC. While pack charge and discharge currents help to minimize these cell-to-cell differences, the cumulative mismatch will only increase unless the cells are periodically balanced. Compensating for gradual changes in cell SoC is the most fundamental reason to balance series-connected cells. Typically, passive or dissipative balancing schemes are sufficient to rebalance the SoC of cells with similar capacities in the pack.