Electric Car Battery Degradation

Electric Car Battery Degradation: Trends, Battery Life, Replacement Cost & More

All batteries degrade over time. Electric car battery degradation is no exception. After thousands of charging cycles, the battery gradually loses capacity. While this can cause alarm for some, prospective electric car shoppers must understand facts. Despite the range lost, the electric vehicle (EV) range may still be sufficient for daily needs. 

This article will review topics such as “How long do electric car batteries last?”, “How to reduce electric car battery degradation?”, “How much does an electric car battery replacement cost?”, and more!

How Long Do Electric Car Batteries Last?

With information available today, electric car batteries last around 200,000 miles. Per a study 6,000 EV study by Geo Tab, electric cars lose about 2% of battery capacity per year. This study includes early Nissan Leafs without TMS. More on that topic later. 

Electric Car Battery Degradation: Geotab
Electric Car Battery Degradation Study Results
Image credit: Geo Tab

Per Electrek, in a sample of only 350 Tesla Model S and Model X vehicles, those specific vehicles still had 90% State of  Health (SOH) after 150,000 miles. State of Health refers to the remaining battery capacity compared to the original battery capacity when new. Lower SOH means less range than when brand new. 

Electric Car Battery Degradation: Telsa Model S and X
Tesla Model S and Model X
Image credit: Electrek

Now, it is impossible to talk about high mileage EVs without bringing up the Tesla shuttle service company, Tesloop. Tesloop’s fleet of Teslas travel hundreds of miles a day. In fact, they have most of the highest mileage Tesla Model S and X with several over 250,000 miles. 

Their highest mile EV is known as eHawk with over 440,000 miles. This particular electric car has had two battery replacements–both under warranty. The first replacement was just under 200,000 miles and the second was just under 400,000 total miles (200,000 miles if restarting the mileage clock from the 3rd battery install).

Electric Car Battery Degradation: Tesloop
High Mileage Teslas
Image credit: Tesloop

Keep in mind that all of Tesloops vehicles sustain several DC Fast Charging (DCFC) through Tesla’s Supercharger Network. More on DCFC later…

How Does the Thermal Management System Protect the Electric Car Battery?

Nearly all electric cars today are equipped with a Thermal Management System (TMS). What this does is monitor and throttle extreme heat from damaging the battery. Apart from general wear and tear of battery cycles, high temperatures, and frequent DCFC affect the electric car’s battery negatively. 

There have been some accounts of older Nissan Leafs in hot climates experiencing quicker battery degradation than normal. Since the Nissan Leaf does not have a TMS, coupled with high outdoor temperatures the battery begins to fail more quickly than usual. 

Thankfully, with TMS the car will activate a cooling system to prevent these hot temperatures from harming the battery. Essentially, TMS is an air conditioner for the battery. Automatically, the EV will enable this A/C when it’s hot outside or DCFC events since high voltage charging results in elevated battery temperatures. 

While manufacturers have designed today’s electric cars to sustain many, many charging events and battery cycles, it is important to remember frequent/daily use of DCFC may accelerate battery degradation. Per CleanTechnica, this point is illustrated by Geo Tab’s study 6,000 electric car battery degradation with DCFC as one of the variables. 

DCFC Impact on Electric Car Battery Degradation
Image credit: Geo Tab/CleanTechnica

As you can see, minimizing DCFC as much as possible has a positive effect on SOH loss. If possible, only use DCFC when needed, such as during long trips. The vast majority of charging should and is by current owners completed through home Level 2 charging. 

How Does a Battery Buffer Reduce Degradation?

While the electric car may show 100% when fully charged, it is actually not 100% charged.

A battery buffer reserves around 5-10% on both ends of the battery in efforts to maintain battery health. The idea is that by reserving battery from actual use, the battery will not complete full cycles, therefore, reducing the degradation rate. This applies to both BEVs and PHEVs. 

For example, the Chevy Volt has a total battery capacity of 18 kWh, however, only 14 kWh is usable. That is to say, once 14 kWh are used while driving, the gas range extender starts up to continue the journey despite some battery capacity remaining.

It is believed that this is the reason why the Volt has had very little battery loss despite high mileage. Chevy Volt owner, Eric Belhmer, is notoriously known on the internet for taking his plug-in hybrid (PHEV) over 400,000 miles with little battery degradation.

Specifically, of the 400,000 miles over 140,000 miles were on the battery alone. Per InsideEVs, Eric’s 2012 Chevy Volt has traveled an impressive amount of mileage with no issues with the battery.

How to Reduce Battery Degradation?

Tip #1: Charge to 70% on a Daily Basis

The simplest way to reduce battery degradation is to only charge to 100% when you absolutely need to. This applies only to BEV (Battery Electric Vehicles or “all-electric”). When you know you will need all of the vehicle’s range, feel free to charge to 100% to complete the journey.

If your typical commute is only 30 miles a day and your EV has a range of 250 miles when fully charge, it’s better to only charge to 70% (175 miles of range). That way, you prevent the battery from fully completing a battery cycle. In addition, you’ll still have over 130 miles of range after your commute for miscellaneous errands, which is more than enough. If you think you need more, feel free to charge to a higher percentage. 

This tactic of only charging to 70% on a typical day does not apply to PHEV (plug-in hybrid) drivers. With PHEVs, feel free to fully drain the battery from 100% on a daily basis. Engineers designed PHEV batteries to be fully charged and fully depleted each day. As mentioned previously, one Chevy Volt traveled over 400,000 miles without significant battery loss or issues. 

With a PHEV, the vast majority of your trips only use the battery, then after the battery charge is depleted, the gas range extender seamlessly starts. If the PHEV battery capacity shortens, then the vehicle simply uses whatever charge is available before using the secondary source of power. 

Tip #2: DC Fast Charge Only When You Need To

Another way to prevent electric car battery degradation is to only DCFC when you really need the range quickly. If you are low on range or see a public charging station available, charge on Level 2 if you have the time. Frequent use of DCFC, as illustrated previously, will accelerate the rate of battery degradation.

Tip #3: Let the EV Cool Down Before Charging

A common tactic EV drivers implement to slow the rate of degradation is to let the EV cool down before charging. After a long commute and possibly a DCFC, the battery will be warm. Feel free to plug the car when you get home, but schedule the vehicle to start charging an hour or two later.

This is similar to waiting for an ICE vehicle’s oil to cool down before changing it. By giving it some time after use before charging, the battery temperature will reduce from an elevated level. Keeping the battery at a neutral temperature is integral to battery health.

In any case, if you charge with Time-of-Use (TOU), that is charging at night when the electricity rates are the cheapest, this cool down period is already factored in your daily charging habits. The car can be plugged in and not charging if you scheduled a delay charge.

Electric Car Battery Replacement: How Much Does It Cost?

It depends on the size of the battery. The larger the battery, the higher the cost. Per Green Car Reports, 2011-2014 Nissan Leafs with the 24 kWh battery pack cost $5,500 to replace. On the other hand, a 2017 Chevy Bolt with the 60 kWh battery pack costs under $16,000 to replace. 

2017-2019 Chevrolet Bolt Battery Pack
Image credit: Chevrolet

Keep in mind that when batteries fail (after 200,000 miles as aforementioned), the entire pack does not necessarily need to be replaced. Sometimes the issue may lie within a few parts. 

What is a Typical Battery Warranty?

Most new electric cars come with an 8 year/100,000 mile warranty. This warranty guarantees a 70% SOH during that time period. Some manufacturers or specific vehicles offer longer warranties such as 10 years or 150,000 miles. Per Tesla:

These warranties cover the repair or replacement necessary to correct defects in the materials or workmanship of any parts manufactured or supplied by Tesla, which occur under normal use.

Closing Thoughts

This subject can be quite controversial since EVs already have a shorter range than ICE (Internal Combustion Engine) vehicles. Additionally, EVs are still a fairly new technology. There hasn’t been a whole lot of information from older high mileage vehicles save for the few hundred Teslas.

Nevertheless, the electric cars that have surpassed 150,000 miles have shown promising results. Additionally, the standard 8 year/100,000 mile warranty handles any issues that come up during that time period. This warranty alone should be enough for most.

Lastly, with data available today, the electric car battery degradation rate of 1-2% per year is very insignificant. If the EV had 250 miles of range when brand new, after 10 years of ownership, the EV would have around 215 miles of range. This loss of 35 miles is insignificant in the real world. 

Moreover, electric car battery chemistry and technology has improved significantly. Manufacturers are beginning to learn the habits of typical driving behavior and the effects of hot climates and DCFC events. Each battery iteration increases battery longevity. For example, Elon Musk promises the most popular electric car, the Tesla Model 3, to last around 300,000 to 500,000 miles as reported by InsideEVs

Electric car battery degradation is, unfortunately, unavoidable. However, with some special technique, battery improvements, and the use of a TMS, the rate of range loss should be minimized.

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