Passive Equalization and the Expiration of Battery Packs on Chinese Electric Bicycles

Passive equalization is applied on valve-regulated lead-acid (VRLA) battery packs of electric bicycles in China. Short cycle life of VRLA battery packs is a big problem for Chinese electric bicycle business. The cycle life of the VRLA battery packs is much shorter than a single battery's although batteries were tested and paired before operating. In 95% of all failed battery packs, only one battery is dysfunctional. Overcharge and over-discharge are the primary factors for the failures of VRLA battery packs. Passive equalization cannot guarantee that the batteries do not over-charge or over-discharge.