Is Fast Charging Bad for Electric Cars?

is fast charging bad for an electric carEver since I read about fast chargers, I wondered if they harm EV batteries. There is a common myth online that fast chargers can decay EV batteries.

But fast charging is trending all over the World, 350kW fast chargers are already operational at hundreds of public charging stations, and soon higher capacity chargers will be available; If fast charging is harmful, then why are they being used and promoted by EV manufacturers?

I studied some research articles to clear my thoughts, and the articles helped me making a decision. Time to finally buy my first fast charger!

Is fast-charging bad for electric cars? Fast charging is not bad for electric cars except in some conditions. In fact, fast chargers can keep your battery healthier than level 2 chargers. But used frequently, fast chargers can harm your battery.

Fast chargers are entirely beneficial when the state of charge (SOC) of Li-ion battery remains within 30-80% range, and the battery temperature remains between 0-30° C. It is recommended to ensure a delay of at least 24 hours between every charge. Fast chargers can be harmful if an electric car is charged three times a day.

Furthermore, not all electric cars are compatible with fast charging. The Li-ion batteries used in old electric cars are not designed for fast charging, they have limited capacity, and their Battery Management System (BMS) is not programmed to manage fast charging. Fast chargers are not beneficial for such electric cars.

Your EV Batteries are Going to Degrade in Any Case!

There is something that you need to understand about EV batteries; whether you use a fast charger or not, the batteries are ultimately going to degrade with the passage of time. They are not going to perform 100% forever. Just the way your cellphone and laptop battery’s performance starts declining after 1-2 years, EV batteries are no different.

Typically the performance of an EV battery starts declining after the first year and falls to approximately 70% after 8-10 years (if handled carefully). Unfortunately, there is nothing you can do about it other than slowing down the degradation process.

Tesla’s Perspective Regarding Fast Charging Implications on EV Batteries

The impact of fast charging on EV battery life has been a myth for a long time. Many EV users believe that fast charging extensively affects battery life, and the BMS is designed to deceive users about battery life. But BMS is programmed to keep reserves in the battery (for enhancing battery life).

The reserved part is not useable, and it protects the battery from completely charging/discharging. Why? You need to learn about “cycle life” and “calendar life” for better understanding. Cycle life means the decay of battery life with completely discharged cycles, and calendar life means the decay of battery life over time.

The decay in EV battery life due to fast charging is strongly linked with cycle life and calendar life. The charging pattern and the environment of battery moderated the impact of fast charging on EV batteries. Certain parameters must be considered when fast charging EV batteries.

Every Li-ion battery starts decaying after its cycle life has been completed, and its efficiency reduces. However, the battery performance will not jump directly from 100% efficiency to 70% but slowly over time. On average, the decay cycles complete at the end of the first year.

Now, if an EV’s cycle life is already completed, the battery is already weak, and fast charging cannot be blamed for further degradation. Similarly, if a battery is already old, although it has not been used much, it is already degrading due to calendar life.

If a battery is already too weak, fast charging may further degrade it, but a new battery’s cycle life can be enhanced if the factors affecting cycle life are minimized. Consequently, fast charging will not decay battery life.

If the state of charge (SOS) frequently remains above 95% or below 2%, it can weaken battery. Here the battery reserve plays its part. The temperature also plays a vital role in charging impacts. Charging at temperatures below 0° C also affects the battery’s life.

Now it is understandable that the charging/discharging pattern and the temperature moderates the result of fast charging. By default, modern fast chargers are designed to ensure that the batteries are not charged above or below safe limits. Such features have made fast chargers safer than ever.

Back in 2006, Tesla proposed that an EV must not be charged in any less than two hours. But the charging mechanisms and Li-ion batteries have improved over time.

Today Tesla has developed a 350kW superfast charger that is capable of charging an EV in 30-60 minutes. Soon 450kW fast EV chargers will jump in the market, but if fast charging has adverse effects on battery life, then why they are being developed? Why not merely stick will slow chargers?

That’s because the game has changed, the latest research has concluded that if appropriately used, fast chargers do not harm EV batteries any more than its predecessors. Besides, charging an EV within a few minutes is far more comfortable then charging overnight.

Modern Research on The Implications of Fast Charging on EV Battery Life 

Since 2014, several research studies have been conducted on the effects of fast charging on EV batteries. The earlier research suggested that fast charging is harmful to EV batteries, but over time the Li-ion batteries improved, charging density enhanced, robust heat management systems, and BMS were designed, and the results changed. Today, fast charging is considered better than slow chargers if appropriately used.

According to the research conducted by Idaho National Labs in May 2018, fast charging has adverse effects but very less. Furthermore, fast charging was less damaging for EV batteries as compared to level 2 chargers (although level 2 chargers are comparatively slow).

A research experiment was conducted on the 2012 model Nissan leaf battery packs. Their performance was tested under different temperatures when charged using a 3.3kW level 2 EVSE and a 50kW CHAdeMO port DC fast charger. The charging mechanism and the performance of batteries were monitored at 20°C, 30°C, and 40°C temperatures.

The point of testing in different temperature ranges was to check if the effects of fast charging vary with temperature or not. Furthermore, the condition of batteries was also monitored under delayed fast charging and vice versa. Surprisingly, results concluded that the delayed fast charging was better than level 2 (slow charging) without delay.

By minimizing longer rest at a high state of charge, the battery life was comparatively enhanced. In case of no delay in fast charging, the battery life degraded by 2-3%.

Fast charging inclined battery temperature, which was leading towards battery degradation, whereas the effects were lower in case of delayed charging.

Battery and BMS Moderates the Effects of Fast Charging

The modern EVs are equipped with robust BMS that is designed to protect a battery from frequent fast charge. For example, if a BMS detects fast charging for the third time within 24 hours, it automatically slows down the charging process.

Not all users are aware of the adverse effects of frequent fast charging, and they may lead their EV batteries to decay before time; the EV manufacturers have programmed BMS to take control in such scenarios and reduced charge rate to a minimum of 1.5 hours of complete charging.

Furthermore, modern EVs are designed for longer routes, which means they have high capacity battery packs. High capacity battery packs are less likely to be damaged as compared to low capacity battery packs. This means the modern EVs are less vulnerable to the adverse effects of fast charging.

Unfortunately, old BMS systems are not designed to carefully handle frequent fast charging, which enables fast charging beyond safe range, leading towards battery decay.

How To Get Maximum Performance From Fast Chargers Without Degrading EV Battery

Here is the takeaway from modern research and EV manufacturers. Fast chargers are useful, but only if you keep the SOC between 30-80%. Doing so will keep your battery healthy and efficient.

The charge drop below 30% affects the health of cells, and frequently dropping charges below 30% can permanently reduce the capacity of an EV battery.

So dropping the charge below 30% is not a good idea. But there is a limitation to the maximum charge level too; EV batteries must be charged maximum up to 80%.

This is because the battery packs start heating up during charging, but the thermal condition starts inclining beyond 80%. High temperatures can also damage a battery’s health.

Apart from that, not charging an EV beyond 80% is actually in your benefit too. How? Ever noticed that laptops and cellphones charge fast until they reach 80% of charging and take more time at charging the last 20% of the battery?

Charging an EV only up to 80% on the fast chargers will also save time. Besides, an average EV user drives almost 50 miles a day, and charging up to 80% can provide enough miles.

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