Why Do Electric Cars Charge Slower After 80% Full? (Explained)

Electric cars depend crucially on battery charging amidst other components to function. However, how you maintain the battery through proper charging practices affects its durability and quality.

In this article, we will look at the reasons electric car batteries charge slower as they get full and if you should fully charge your car battery.

Also, we will explore if slow charging is better than fast charging, and what to expect in the future concerning electric car battery charging rates.

The Reasons Electric Car battery Charge Slower:

Your electric car battery charges slower because of many reasons. One of them is so your electric car can control the power it draws from the source. While charging, your electric car tries to charge the more depleted cells while making sure it does not overcharge the fully charged cells.

This can occur at the start of the charge or when the charge reaches a certain percentage while charging your battery, depending on the car model.

Also, low temperature slows down charging by restricting the speed of power transfer. In certain cases where your battery charges slowly, it may be because the temperature your battery charges at is low.

Why Do Electric Cars Charge Slower After 80%?

Electric cars charging slower at 80% is a normal attitude in most electric car models. It does this because the charger is restricting the speed the battery charges to protect it from overheating.

Your battery will charge at a higher speed when it is nearly empty because the charger is supplying the complete current when the percentage of the battery is lower. However, when it reaches 80%, the current your battery takes will drop.

The current drops because the heat your battery generates at this stage gets higher, unlike at the onset of charging.

At this point, the ions in the battery need stabilization. The charger reverts to slow charging for the remaining 20% so your battery can perform at the optimal level. This also helps preserve the lifespan and health of your battery.

In most electric cars, the remaining 20% of the charge can take as long as the previous 80% charge to complete. It is mainly because your electric car manufacturers designed their battery for maximum longevity.

However, the slower charge of your battery after 80% is to protect it from the heat of fast charging.

Why Do Some Fast Chargers Stop at 80%?

Some fast chargers stop at 80% to protect the battery in certain cases. There have been many verified claims that Lithium-ion batteries do not do well when they experience high voltage consistently. This can cause them to degrade faster. 

In this situation, car owners may program their cars through the settings to stop charging at 80% to protect the lifespan of the battery.

It’s simply a bad idea to always charge a Tesla to 100%.

Also, some fast charge stops at 80% because some charging point operators cut off power at this point. Some limits may be up to 90% or 95% depending on the limit the operator has set.

They do this because it takes the same period your battery will charge from 80%-100% as the period it charged from start to 80%.

In situations where other electric cars are waiting to use the same charging point, waiting for a car to fully charge beyond 80% will take longer. It may also limit the number of cars that have access to power their EV at this charging point.

And in situations where there is a long queue with some car models that take longer than the average period to charge, and with limited charging points, some may not have access to charge for days.

To make room for other electric car owners who want to charge to have access to the charging point in time, the charging point operator may program chargers not to charge beyond 80%. Thus, the rapid charging will power as many electric cars as possible within a short period.

Should You Avoid Charging Electric Cars to 100%?

Charging your electric car to 100% on certain occasions is something you may need to do, especially in situations where you intend to drive the car soon and need its full range.

But frequently charging it to 100% and making it hold a charge of 100% for a long period is something you should avoid. This practice can expose your car to frequent overheating, which is detrimental to the battery’s health.

Michigan School Of Environment and Sustainability has reported that spending a long period at extremely high and low charging states (100% or 0%) stresses the battery. Also, battery experts have mostly recommended 80% charge for optimal battery lifespan.

However, there are also claims that you can charge your battery to 100% as automakers make modern electric cars with a smart system that regulates them to have a healthy charge. These electric cars have a built-in buffer that won’t allow the car battery to charge up to 100% or deplete to 0%.

Automakers programmed this smart system in electric cars to tell the battery is full. But the battery has only charged lesser than the maximum capacity to preserve its lifespan. Just like it will depict a low battery when it still has some juice in it.

So, it may not bother you to charge your car to 100%, but be certain your car has a built-in buffer.

Also, the charging recommendation varies for each auto manufacturer. According to the Globe and Mail, Ford and Volkswagen recommend a 100% charge when you need your car’s full range for longer trips.

For daily driving, Volkswagen recommended an 80% charge and Ford 90%. Nissan stated there is no problem charging to 100% every time car owners charge them. However, Tesla made no response.

Also, some car models have a setting which allows you to set your EV to stop charging at a certain percentage.

For a better charging experience, consult your automaker for the best charging practice for your car. This is because charging recommendations vary for each car model.

Related: Why Do Charging Electric Cars Take So Long? (Explained)

Is Slow Charging Better Than Fast Charging?

Slow charging is better than fast charging because it charges the battery at a lower speed, which benefits the long-term health of your electric car battery.

It accomplishes this by reducing the heat and pressure that accompanies charging your battery.

Slow charging may take longer to charge your electric car battery than fast charging. And, it may benefit cars that charge at night and work during the day more, but we recommend car owners should adopt it as it protects your car battery from deteriorating quickly.

However, unlike slow charging, fast charging uses DC charging, which is greater than the voltage of the battery. This can cause the fast degradation of your battery and can lead to the damage of some internal components from the increased thermal load.

Also, because it charges your car battery in high heat to make the charge fast, it can cause the battery to overheat quickly and eventually fail.

According to AE Electronics, slow charging makes your battery life cycle over 3000 times more, while fast charging shortens it to about 1000 times or lower.

Related: Leave Electric Car Running While Charging? (Basic Guidelines)

Will an Electric Car Charge Slower the Older It Gets?

Your electric car may charge slower as it gets old. This is because electric car batteries degrade and may lose their capacity to charge effectively.

However, this depends on your car battery’s ability to handle deterioration. Some cars may not hold power as they used to, while others can hold power well as they deteriorate.

Note that the period electric cars last as it deteriorates even with proper maintenance differs from model to model. While some automakers specified the time frame in their manual, some may not. But your car battery charging slower may be a sign that accompanies your car as it ages.

However, the slow charging rate may be worse and even start earlier in situations where car owners didn’t manage their batteries effectively.

This is the reason we recommend slow charging over fast charging. And in situations where car owners can’t avoid fast charging, they should avoid charging the battery beyond 80% to preserve its lifespan.

While batteries with a longer lifespan make electric cars last longer, it also helps maintain the ability of your car to keep its charging capacity without diminishing over a long period

Do Electric Cars Lose Charge Capacity Over Time?

After much charging and discharge cycle, an electric car battery may lose its charge capacity slowly over a long period. While the degradation happens gradually, it is unlikely it will fail altogether.

Most electric cars will lose some percentage of the charge capacity they can hold after certain miles. However, these miles are small and only get higher after several miles.

For example, according to a report from Plug-in America, Tesla Model S only loses five percent of its original charge capacity after reaching 50,000 miles. However, the rate of depletion will gradually slow down from this point.

Also, the rate and miles cars lose charge capacity differs from car to car. Whichever it may be, automakers have a warranty that lasts a minimum of 100,000 miles.

Only Hyundai provides a lifetime warranty for electric car batteries so far. Note that automakers offer these warranties based on certain conditions.

However, while it varies for each car manufacturer, some factors can cause a car to lose charge capacity quicker aside time. They include hot temperatures and excessive use of fast charging points. Thus, electric car owners should avoid these factors so their battery can meet expectations.

Related: Do Tesla Superchargers Cost Money To Use? (Explained)

Should We Expect Faster Charging in the Future?

Researchers are closing in on a battery that can charge in 10 minutes or fewer, so we should expect much faster charging in the future.

So far, a team of Harvard scientists has recently designed a long-lasting, stable, and quick-charging lithium prototype. The battery under laboratory conditions can recharge over 50% of its capacity within 3 minutes. Also, the battery will charge and get discharged 10,000 times.

The battery can also increase the lifetime of electric cars by 10-15 years without the need to change the battery. It will also pave the way for electric vehicles that can charge within 10-20 minutes.

Another improvement in electric car batteries is from battery companies so far. Many companies have been trying to develop new batteries that can fast charge at a higher rate and will remain stable. So far, these companies can also place 20 minutes or lesser on the charging period of their batteries.

One of these companies is Echion, which is producing new lithium-ion car battery material that enables super fast charging. While they did not mention the duration of each charge, batteries are safe and have high energy density.


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