Nature Energy reported that cell-to-cell inconsistency shortens battery pack lifetime by 17.7% in passenger cars and 22.8% in electric buses compared to the average lifespan of their individual cells.
Researchers evaluated operational records from 116 electric passenger cars using nickel-manganese-cobalt batteries and 17 electric buses using lithium-iron-phosphate batteries. The monitoring spanned more than three years, with individual vehicles logging up to 300,000 kilometres.
Cell variations reduced usable pack health by 6.2% in cars and 7.5% in buses because the most degraded cells restricted total pack capacity. Resistance disparities between cells also reduced available power capability by 12.9% for passenger cars and 15.1% for buses.
Passenger cars used 80.7% of their total available energy resources over their operational lifespans. Electric buses achieved 72.9% energy utilization before reaching retirement thresholds.
Fleet tracking data
Analysts sourced the operational data from the National Monitoring and Management Centre for New Energy Vehicles. The resulting dataset comprised 587.5 million rows of real-time operational measurements gathered at a nominal frequency of 0.1 hertz.
Data preparation removed records from vehicles with initial mileages above 100,000 kilometres or insufficient operational history. The team identified slow, long-duration charging events across wide state-of-charge windows to calibrate individual cell capacity estimates.
Degradation patterns
Measurements showed that cell health variation remained low across passenger vehicles up to approximately 170,000 kilometres. Beyond that threshold, multiple vehicles showed widening health disparities as individual cells entered accelerated degradation phases.
Neural network models projected cell capacity and resistance metrics onto a standardized reference temperature of 27 degrees Celsius. In a representative passenger car cell, an accelerated ageing knee point emerged past 240,000 kilometres.
