EV Battery Pack Life: Pack Degradation and Solutions 951949

Several lead-acid battery packs of different manufacture and voltage were evaluated on a performance and life-cycle basis. The battery packs ranged from a small 36 volt laboratory pack to a 320 volt full size U.S. Electricar S-10 truck pack. The influence of the charge algorithm, ambient temperature, and module connection methods for parallel strings on the performance and cycle-life of this laboratory pack was studied. Finally, a survey of presently employed battery management techniques, used in three “production” electric vehicles, was conducted.

A standard set of testing procedures for electric vehicle batteries, based on industry accepted testing procedures, were used in the evaluations. The battery packs were evaluated by a combination of constant current capacity tests, cyclical loading to simulate typical EV driving cycles and actual EV driving experience.

The results of these experiments should help electric vehicle and battery manufacturers understand and design battery management systems that will reduce pack degradation. It is the feelings of the authors that the Battery Management System (BMS) must be able to prevent module damage and pack capacity imbalance. We do not feel that a BMS system can fix damaged modules. Further, the system must be reactive to prevent damage and to be able to accept replacement modules. The system must be flexible (programmable) and have the ability to learn about the pack. The BMS must be able to interface with proper chargers (high power) and inverters/controllers; optimally it would be best to integrate the inverter, charger and BMS. The BMS should provide driver and maintenance information such as: State of Charge (SOC) and range available, bad modules and module temperature.