Electric cars: How many kilowatt hours does the battery actually offer?

After two years, the traction battery of Christian Stadler’s VW ID.3 delivers 50.4 instead of the 58 kWh originally specified by the factory. This corresponds to a degradation of 13 percent. Stadler runs the Battery Life YouTube channel and knows its ID.3 through and through. To verify his calculation, he makes the professional one Test by Aviloo. The Austrian company enables every owner of an electric car to carry out a certified degradation measurement themselves. The result is similar: 50.26 kWh are left, says Aviloo, but only speaks of a seven percent loss. Further calculations of possible measurement errors, for example due to an inaccurate odometer in the VW ID.3, only lead to minimal changes. In principle, it is therefore clear that the traction battery has aged. A blur remains. What’s going on here?

Traction batteries in electric cars wear out over use (cyclically) and over time (calendarly). The manufacturer’s warranty periods therefore relate to a number of kilometers – which results from the number of expected cycles multiplied by the range – and a number of years. Typical are, for example, 160,000 km or eight years. The warranty conditions of the car industry always contain an assumed aging; usually 70 percent of the new condition is the limit.

The values ​​published by the manufacturers are not yet subject to any legal definition. The terms are also often not used in a transparent and understandable way for normal people. One example is battery capacity: Strictly speaking, it is the number of ampere hours (Ah) that can be charged or discharged. BMW, for example, had always correctly spoken of Ah with the i3. However, as with electricity consumption, the unit kilowatt hours is common. This results when the voltage is taken into account in addition to the ampere hours. When talking about kWh, technically correctly formulated, the energy content is meant. In the configurator, Volkswagen writes “net energy content 58 kWh” for the ID.3.

The measurements by Christian Stadler and Aviloo almost agree. The fact that Aviloo comes up with only seven instead of 13 percent degradation is due to another basic assumption. We spoke to Nikolaus Mayerhofer, Chief Technology Officer (CTO) and extremely experienced in dealing with battery systems. He explains that Aviloo’s measurement either goes to 0 percent charge level or 0 km remaining range. In the case of the ID.3, this resulted in 54 and not 58 kWh. If the electric car continues to drive afterwards, this is not taken into account.


VW

VW

Volkswagen correctly speaks of “net energy content” in the configurator. The battery capacity indicates how many ampere hours can be charged or discharged. The energy content also takes into account the voltage curve.

heise/Autos has further measurements that electric car owners have made with the Aviloo test. A Cupra Born (test) confirms the ID.3’s initial energy content of 54 kWh, and a Hyundai Ioniq 5 was only assumed to have 68.9 instead of 72.6 kWh. Apparently, to protect components, the manufacturers are cutting the amount of energy that can actually be drawn or what is visible to the driver. One aspect of this is keeping a few remaining kilometers below the 0 percent display as a reserve in order to avoid getting stuck at a critical section of the road. There is often a buffer at the top end too. One thing is certain: If you want to save your traction battery, you can limit the charging window voluntarily.

Nikolaus Mayerhofer from Aviloo gives important tips on this: “I treat the battery best if I keep the charge level at 50 percent. The battery feels better if it is charged from 40 to 60 percent instead of from 20 to 80 percent, for example. The closer and the longer you are to the 0 or 100 percent limits, the worse it is for the service life.” Aviloo can imagine publishing the energy content of individual or all electric cars in the database in the medium term. That would be a huge win for consumer protection because potential buyers want to know what they’re getting into.


Tesla

Tesla

Tesla completely dispenses with the specification of an energy content. There is no statutory provision on this. On the other hand, the range specification is regulated according to WLTP – and Tesla adheres to it.

The electrical energy that can be drawn from a traction battery is less easy to define than the volumetric tank capacity for fossil fuels. There are slight fluctuations in temperature with them, nothing more. In the case of electric cars, no uniform regulation can be identified as to what content the manufacturers specify in the data sheet. Tesla doesn’t do that at all. In addition, the change over temperature – especially in the cold – and also over the lifespan are much larger. In addition, it is no secret that manufacturers can use software updates to limit the charging window of an existing electric car or its charging capacity afterwards.

Certified measurements of the SOH (State Of Health), such as those being initiated by Aviloo or Twaice, where the Battery Quick Check will soon be offered, are elementary for the future electric car market. In a year’s time, no used car buyer will probably accept a simple reading of the onboard diagnostics for the SOH. Certified measurements will be the rule – and lead to disputes.

Not every vehicle owner of an electric car is aware that the traction battery degrades at all. The spectrum of aging will also be very different. Some will have little wear even after years. Others may be able to draw significantly fewer kilowatt hours from a year-old car than the data sheet once promised. Still others will experience that there will be defects.



Aviloo enables electric car owners to determine the exact degradation of the traction battery themselves. The company assumes the loading window up to 0 km remaining range as 100 percent; should the electric car be able to drive a few more kilometers – for example for safety reasons, to prevent it getting stuck in a critical spot – this does not count at Aviloo. The VW ID.3 only has 54 kWh left.

Above all, there should be irritation about the battery guarantee. Because if the remaining capacity falls below the guaranteed 70 percent, for example, the customer does not get a new memory. Manufacturers will then bring the battery into the guaranteed SOH range, for example by replacing individual modules. Before that, there will certainly be discussions about the exact status of the degradation – different test results from contract workshops and independent experts will still occupy the courts.

The causes of the degradation itself are manifold. Usage behavior has an influence, but so does the quality of the battery system itself: Is there complex and active temperature management for cooling and heating or not? Did the manufacturer have to allow a relatively large loading window from the outset out of consideration for the costs, i.e. a lot of the net amount compared to the gross? Which cell chemistry was used? LFP cells, such as the basic versions of Tesla Model 3 (test) or MG4 electric (driving report), for example, are more cycle-resistant than the currently widespread NMC cells. Like so many aspects of electromobility, the extensive practice that has been collected over more than a hundred years with combustion engines is missing. The learning curve is particularly steep now, in the initial phase.


(mfz)

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