Electric car: Charging above 80% can be counterproductive

Habits die hard: Some electric motorists are still trying to “refuel” at fast charging stations. However, this is a counterproductive idea that can create unnecessary expectations for other electric cars, especially at larger departures.

With departures on holiday, this summer 2022, and the first traffic jams at fast charging stations, we realize that many motorists have not yet understood how to optimize their charging. Many people consistently seek to charge the battery up to 100% or close to that value. This method can waste them time or money (depending on charging station prices), in addition to creating unnecessary waiting time at a charging station for other users.

Tesla owners have already gotten into the habit of charging only what is needed to continue their journey, greatly aided by their car’s scheduler. For the others, there is definitely a lack of training in car delivery combined with fear of crashes. However, this attitude leaves other users of these charging networks confused.

Charging time was sometimes doubled

In some cases, 100% charging is legal. Let’s avoid any misunderstanding: We do not tell you not to do it or that it is bad for your battery if you do. It’s just that it’s now inappropriate and time consuming. In most cases, a charge of 80% is enough to calmly continue your journey until the next charging session.

It often takes as long to charge the battery from 20 to 80% as it takes to charge the remaining 20%. The closer you get to 100%, the more the duration can be extended until it seems infinite when you are at a terminal that is supposed to be fast. The last electrons that we put in the battery are a bit like the last drops that we put in the tank after “clicking” on the fuel nozzle.

The charging power decreases after 80%. // Source: Raphaelle Baut for Numerama

If the concept of charging curve is mastered by some owners of electric vehicles, this concept is totally unknown to some beginners. This sometimes pushes you to engage in some surprising behaviors, such as stopping to charge when you have 70% battery left. It will take much longer to recharge these 30% than to do so when the battery is at 50% or less.

But what is the charging curve?

The charge curve is the power current that is theoretically accepted by the battery, depending on its charge level (Soc). It is specific to each electric vehicle and depends on the choices made by the vehicle manufacturer.

For the brand, the idea is to find the best compromise between recharging speed and battery cell durability. The recharging effect can be deliberately limited by the manufacturer’s care to prevent the cells from overheating during charging. This sometimes explains why a car after an update of the vehicle’s software can see its charging speed increase, even though there has been no physical change in a part connected to the car’s battery.

However, the charging curves almost all have one thing in common: their drop is staggering the closer you get to 100%.

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Example of charging curves of 4 models on the Fastned site. // Source: Capture from the Fastned website

It would probably be useful for manufacturers who communicate more easily about the maximum charging effects to also indicate the charging curve that comes with the vehicle. This would certainly allow customers to better understand why the charging station, given to 350 kW, only distributes to their vehicle a maximum of 70 kW before it collapses to 15 kW.

The fast charging operator Fastned has published the charging curves for many vehicles in circulation in the FAQ on its website. The Automobile-Propres website also distributes a charging time simulator that also represents these charging curves.

For more electrical efficiency, we use the chip jump method

Let’s not forget that the break is important every two hours! This is good, it generally corresponds to the moment when a charge can be welcome, for an electric vehicle driving on the highway at a speed between 110 and 130 km / h. This of course depends on the capacity of the battery you have.

If this method was still difficult to use calmly a few years ago, especially outside the network of Tesla superchargers, the network of fast charging stations is now more developed to do so. If your vehicle does not have a trip planner, the Chargemap, ABRP or Chargefinder applications can help you prepare for your trip and find free charging stations.

To optimize the pause time, and if the vehicle has this option, do not hesitate to activate the preheating of the battery. A battery that does not have the ideal temperature (too hot or too cold) when charging will find that its recharging power is greatly reduced from its capabilities.

By avoiding unnecessarily occupying a terminal beyond what is necessary, recharging on long journeys can only go better for everyone. Unfortunately, there will always be a problem with the reliability of the terminals, which can find itself with a limited flow or even worse, completely out of operation.

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