Plug-in wheelchair accessible vehicle grant: preparing battery degradation evidence
Published 14 June 2022
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The applicant must demonstrate that the battery or fuel cell used to drive the vehicle’s propulsion system has an acceptably low rate of degradation.
As a guide to applicants, pending the evidence presented in each case, an acceptable level of degradation is defined as:
For battery electric vehicles:
- the battery must maintain at least 80% of its initial or rated charge capacity for the initial 3 years, or
- 70% of initial or rated charge capacity for the initial 5 years
For fuel cell vehicles:
- the fuel stack must maintain at least 90% of its rated voltage output for the initial 5 years
Given the newness of this technology, we are prepared to work with manufacturers who supply alternative evidence which provides what the Vehicle Certification Agency (VCA) judges to be a reasonable level of reassurance to the consumer.
Assessing evidence
In cases where the applicant is providing written assurance that the battery will offer reasonable performance, the evidence provided may be in the form of:
- illustrative evidence of the degradation rate under certain conditions, such as under an accelerated testing regime
- a supporting explanation of the way in which this evidence demonstrates long term maintenance of the performance
The VCA may consider the following elements listed as indicators of quality sufficient to offer reasonable performance during normal use.
In this context, they will consider what is appropriate to the vehicle and range/performance stated by the manufacturer.
The applicant may wish to identify the possible failure modes and mitigating actions that have been taken.
As a guide to the level of detail expected, we would not expect the evidence submitted to require more than ten pages. Annexes can be provided if desired.
The VCA or supporting independent technical experts may request additional information to inform assessment of the application.
What will be assessed
The types of indicators or factors which the VCA and independent technical experts will take into account when assessing this evidence are:
Battery cell
Data at the cell level can include the published test data of cell manufacturers.
Transportation
Conforms to UN Manual of Tests and Criteria Rev.7 (2019) and Amend.1 (2021), Part III, Chapter 38.
Cycling tests
Provide appropriate evidence, to represent the final application of:
- c-rating
- depth of discharge
- influence of temperature on characteristics
Self discharge rates
Values and method of establishing them.
Impedance
Measurement method and evolution with both elapsed time and use.
Capacity
Measurement method and evolution with both elapsed time and use.
Battery pack
Evidence needs to clearly show how the cells have been combined to produce performance in a battery pack that meets the stated specification.
Mechanical integrity
- resistance to stresses caused by dimensional changes of cells in operation
- vibration, strength and damage testing that has been performed
- strategy for preventing and containing effects of cell failures
Thermal integrity
Provide a summary of your thermal management strategy and how it is achieved, such as, for example, cell-to-cell temperature variation and overall pack temperature control
Cycling tests
- are the tests appropriate to the claimed usage of the vehicle?
- are the cycling profiles, ratings and temperatures of the tests appropriate?
Environmental resistance
- what is the intellectual property (IP) rating of the pack?
- resistance to dusts and liquid and gaseous contaminants
- resistance to extremes of temperature
Battery management system
How does the battery management system (BMS) ensure that the individual cells are not required to operate outside of its specification?
Fire performance
Is there a report that confirms appropriate testing has been carried out?
Vehicle
The integration of a battery pack into the operational context of a vehicle can impact the battery degradation rate. How has this been considered by the manufacturer? In addition to the following points, the issues considered at the pack level should also be addressed at the vehicle level.
Battery management system
How does the BMS ensure that the battery pack is not required to operate outside of its specification?
Thermal integrity
What cooling strategy has been put in place to support the operation of the battery in the UK environment?
Onboard diagnostics
What error and information messages will be provided to the driver on the status of the battery? What error messages will be recorded for maintenance?
Dirt, dust and water ingress and mechanical stress
What measures have been taken to assess and control these factors?