(EU) 2023/1542 · Annex XIII(4)(a) -> Annex IV, Part A(2)
Power and power fade: why the cell datasheet does not cover it
Of the five parameters in Part A of Annex IV, power is where industry usage and the legal term drift furthest apart. Datasheets quote peak and continuous power at some state of charge and temperature. The Regulation defines power as the amount of energy a battery is capable of providing over a given period under reference conditions, and asks for fade alongside it — a figure that only comes out of ageing. The first number is usually somewhere in supplier documentation; the second was often never measured at all.
How the Regulation defines power
Point 3 of the introductory part of Annex IV provides that power means the amount of energy a battery is capable of providing over a given period under reference conditions. The value is stated in watts under point 2 of Part A. Because the definition hangs on a period, a figure without that period cannot be checked: 3 kW for ten seconds and 3 kW for thirty minutes are two entirely different claims about the same battery, and they look identical on paper.
Power fade needs a second measurement, not a second opinion
Point 4 of the introductory part of Annex IV defines power fade as the decrease, over time and upon usage, in the amount of power a battery can deliver at the rated voltage. The percentage therefore compares two states of the same battery — not two products and not two cell lots. This is the part of the field that cannot be transcribed: it only comes out of an ageing test that takes real time, and a typical development programme does not run one before start of production.
Public power and restricted power are different numbers
Point 1(i) of Annex XIII asks publicly for original power capability in watts and its limits, with temperature range when relevant. That is a model-level figure at the starting point. Point 4(a) instead asks for the values of the Article 10(1) parameters for the individual battery, both when it is placed on the market and when it is subject to changes in its status. One number cannot serve both: the public one describes a model at its origin, the restricted one describes a unit along its life.
What has to travel with the value
Article 10(1) requires the technical documentation to explain the specifications, standards and conditions used for measurement, covering at least the elements of Part B of Annex IV. Three of them speak directly to power: the applied discharge and charge rate, the ratio between nominal battery power in watts and battery energy in watt-hours, and power capability at 80% and 20% state of charge. Without those three, a wattage figure is not comparable between suppliers.
Where it goes wrong
- Copying peak power from the cell datasheet; the Regulation speaks of the battery's power under reference conditions and over a given period.
- Stating power without the period it refers to — the Annex IV definition is explicitly tied to one.
- Leaving fade blank because no ageing test was run; a number with no measurement behind it is not a way out.
- Reusing the public point 1(i) value for an individual battery, although the level and the moment are both different.
Frequently asked
How does the Regulation define power?
Point 3 of the introductory part of Annex IV: the amount of energy a battery is capable of providing over a given period under reference conditions. The value is stated in watts under point 2 of Part A.
What does the fade percentage refer to?
To the decrease, over time and upon usage, in the amount of power the battery can deliver at the rated voltage, as defined in point 4 of the introductory part of Annex IV.
When must these values be stated?
Point 4(a) of Annex XIII requires the Article 10(1) parameter values when the battery is placed on the market and when it is subject to changes in its status. The Article 10(1) document itself has been mandatory since 18 August 2024.
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