How to maximise the life of EV batteries
Simple steps could add a year to the life of EV batteries
New research has shown how fleets and their drivers can minimise the battery degradation of electric vehicles by pursuing smart charging strategies.
The study by the EV-elocity project, funded by the UK Government, found that simple initiatives could significantly improve the battery health of hard-working fleet EVs compared to a conventional ‘dumb’ charging approach, which charges batteries to 100% capacity regardless of when a vehicle will next be used.
Typically, battery capacity declines due to both the age of a vehicle and the number of charging cycles.
Ageing is mostly impacted by the battery storage temperature, the state of charge (SoC) in batteries, and how long batteries spend in a resting state; whereas decreased performance due to charging cycles depends on ambient temperature, the number of charge cycles, the speed of charger used and the depth of discharge.
The research discovered that where a vehicle is heavily used and the state of charge in its batteries is typically lower when it is plugged in, a time-shifted approach that ensures the batteries only reach 100% charge capacity when the driver is ready to set off again: “is the simplest and most effective way to protect the battery.”
This improved battery life by 14.9% over one-year of continual operation, compared to a ‘dumb’ charging strategy of plugging in the vehicle as soon as it is parked. An improvement on this scale is equivalent to an extra year of use from an EV, said the report.
One basic step that EV fleets and drivers could implement is to keep batteries neither at full nor very low states of charge. Leaving vehicles with a high state of charge in their batteries decreases their capacity.
Ambient temperature also has an impact on battery health, although there is less opportunity for fleets to control this.
The study assessed the impact of five charging strategies on battery health:
- Standard charge strategy: the EV battery is fully charged as soon as it is connected to the charger, then left at 100% SoC until the driver sets off.
- Time-shifted charge strategy: the EV battery is left at SoC and only charged at appropriate time to reach 100% capacity when the driver sets off.
- Battery pre-conditioning: the EV battery is left resting at the optimum SoC to minimise the ageing rate, and then charged at an appropriate time to reach 100% at when the driver sets off.
- Battery pre-conditioning via vehicle-to-grid: EV battery is discharged via vehicle-to-grid bi-directional charging to the SoC with the lowest ageing rate, and then charged at an appropriate time to reach 100% when the driver sets off.
- Combined smart charge V1G and V2G (SC VxG): A combination of SC V1G and SC V2G that considers the trade-off having extra cyclic ageing via vehicle-to-grid to achieve optimal SoC while minimising calendar ageing.
Despite the extra ‘ageing’ of constantly charging and discharging batteries through vehicle-to-grid systems, the study also found that blending vehicle-to-grid with a strategy that charges batteries to 100% only when a vehicle is ready to be driven can still protect the health of batteries more than dumb charging.
Chris Rimmer, Infrastructure Strategy lead at Cenex and the project’s lead project manager, said: “Our conclusions show that it is not necessary to trade-off financial, environmental and asset lifetimes when charging electric vehicles. Cost, carbon, and conditioning benefits can all be gained when V2G is used intelligently with fleet vehicles.”