Charge Your EV to 80 or 90%? The Great Debate Settled

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EV charging: 80% vs. 90% for battery health and range. Optimize your EV's mileage and longevity.

Electric vehicles (EVs) have become increasingly popular in recent years as drivers look for alternatives to gas-powered cars. A key component of EVs is their battery, which powers the electric motor. EV batteries work a bit differently than gas tanks – instead of filling up all the way, most experts recommend charging to 80% or 90% to optimize battery life.

But is there really a difference between charging to 80% versus 90%? What are the pros and cons of each approach? This article will provide an overview of EV battery basics, explain the differences between 80% and 90% charges, and offer recommendations on the best daily charging habits for your EV battery. With the right charging approach, you can maximize driving range while also extending your EV battery’s lifespan.

Battery Basics

Lithium-ion batteries power most modern electric vehicles (EVs). They work by moving lithium ions between a positive and negative electrode when charging and discharging.

The positive electrode is made of lithium metal oxide while the negative is made of graphite or silicon. An electrolyte allows the lithium ions to flow between the electrodes. Charging forces the lithium ions to the negative electrode while discharging pulls them back to the positive side.

As the battery charges and discharges through these cycles, the electrodes gradually wear down through unwanted chemical reactions. After hundreds or thousands of cycles, enough degradation occurs that the battery can no longer hold a full charge.

The rate of degradation depends on factors like battery chemistry, temperature, and the depth of discharge on each cycle. In general, lithium-ion batteries last longer when kept cool and charged to lower levels per cycle.

80% vs 90% Charge

Charging your electric vehicle’s battery to 80% or 90% has its advantages and disadvantages that are worth considering.

Pros of Charging to 80%

  • Reduces strain and degradation on the battery by avoiding the top 20% charge. This part of the charge causes the most wear.
  • Extends the battery’s lifespan and capacity over time. Partial charges put less stress on the cells.
  • Provides a buffer to account for public charging past 80%. If you charge to 80% at home but a public charger takes it higher, you still avoid the 90-100% wear zone.
  • May provide slightly better driving range in very cold weather. The top part of the battery capacity is more impacted by temperature.

Cons of Charging to 80%

  • Reduces your driving range per charge. You won’t be able to utilize the full battery capacity.
  • Requires more frequent charging sessions to maintain charge levels.
  • Can cause “range anxiety” if your daily driving needs exceed the reduced range.
  • Less cost effective if your electricity rates are very low or you have free charging.

Pros of Charging to 90%

  • Maximizes your driving range per charge. You can fully utilize the battery capacity.
  • Requires less frequent charging sessions. Every charge takes you further.
  • Minimizes range anxiety since you get the most range the battery can provide.
  • More cost effective if electricity rates are very inexpensive. You use more of the available battery per charge.

Cons of Charging to 90%

  • Causes the most strain and degradation on the battery by fully charging to 100%.
  • Reduces the battery’s lifespan and capacity over time. Frequent full charges wear the cells.
  • Provides little buffer for public charging past 90%. Even occasional full charges wear the battery.
  • Slightly reduces winter driving range. The top battery capacity is reduced.

Battery Degradation

Overcharging an electric vehicle battery can accelerate battery degradation and reduce battery life. Most lithium-ion batteries used in EVs today are designed to have a lifespan of 5-10 years or around 100,000 – 200,000 miles. However, improper charging habits can shorten this lifespan.

When an EV battery is charged up to 100% and kept at that state of full charge, it puts strain on the battery’s internal chemistry. The high voltage forces lithium ions into the anode material, causing buildup over time. This added stress can cause faster capacity loss and lower the total lifetime charge cycles.

Aim to charge to 80-90% for daily use, and only charge up to 100% when needed before longer trips. Avoid leaving the battery at 100% charge for extended periods. The sweet spot for lithium-ion battery longevity is keeping the charge level between 20-80% as often as possible.

Maintaining the battery between a partial rather than a full state-of-charge reduces the speed at which battery capacity degrades. Most EV manufacturers recommend charging daily to 80% or 90% for optimal battery health over the vehicle’s lifetime.

Daily Driving Habits

Electric vehicles have significantly lower daily driving needs compared to gas vehicles. Studies show that the average person drives 29-36 miles per day. With most EVs having ranges of 200+ miles per charge, an 80% daily charge would easily cover the average driver’s needs.

Charging to 90% instead provides extra buffer which could be useful for some. But it’s unnecessary for many drivers. Those with consistent, shorter commutes likely don’t need to go above 80%. Going to 90% makes more sense for those with variable and longer daily drives.

The key is to look at your average daily mileage and choose a target charge level accordingly. If your regular daily driving is within 30-40 miles, an 80% charge will suit you well. If your driving is more inconsistent and averages 50+ miles per day, aim for 90% instead. Monitor your driving and charging habits for a few weeks to determine the optimal level for your lifestyle.

Home Charging

When charging your EV at home, you have two main options – Level 1 and Level 2 charging.

Level 1 charging uses a standard 120V household outlet. This provides about 3-5 miles of range per hour of charging. Level 1 is the slowest charging speed, but requires no additional equipment beyond the EV’s included charger. It’s a good option for plugging in overnight if you don’t drive long daily distances. The drawback is that fully recharging can take over 24 hours.

Level 2 charging requires installation of a 240V outlet, similar to those used for large appliances like dryers. This provides 10-20 miles per hour of charging, allowing a full charge overnight in most cases. Installation costs vary greatly based on your electrical panel’s location and amperage capacity, ranging from $500-$2000. Level 2 charging provides the best blend of charging speed and affordability for daily home use.

When deciding between Level 1 and Level 2 for home charging, consider your average daily driving needs. Level 1 works for low mileage commuters. But Level 2 is preferable for most, providing faster charging to allow completing longer trips and tasks without range anxiety. Evaluate the convenience and costs of installing Level 2 in your garage or driveway to make the most of home charging capabilities.

Public Charging

Public charging stations are becoming more widely available, which makes EV ownership more convenient. Major charging networks like Electrify America, EVgo, ChargePoint and others are rapidly expanding their infrastructure. There are now over 100,000 public charging ports in the US, with new ones being added daily.

Many workplaces, shopping centers, restaurants, hotels and other businesses are also installing charging stations for customers. Apps like PlugShare and Chargeway allow you to locate stations along your route and check real-time availability.

While public charging is not as fast as home charging, it can still provide 20-30 miles of range per hour. This makes it feasible to top up your battery while running errands, eating a meal or even while parked at work.

The convenience of public charging helps alleviate “range anxiety” – the fear of running out of charge mid-trip. Knowing you can stop and charge along the way gives EV owners more confidence for longer drives.

As the charging infrastructure continues to grow, range anxiety will become less of an issue. Most drivers will be able to rely on a combination of home and public charging to meet their daily mobility needs.

Battery Warranties

EV battery warranties provide peace of mind for many drivers. Most automakers provide lengthy warranties that cover the battery pack for defects and significant degradation. This gives EV owners confidence that the battery will perform as expected throughout the warranty period.

EV battery warranties typically span 8-10 years or 100,000 to 150,000 miles. Some automakers even offer longer warranties up to 200,000 miles. The warranty covers repairs and replacements needed if the battery capacity falls below a specified level, usually around 70%.

For example, Tesla provides an 8 year/100,000 mile warranty that guarantees at least 70% battery capacity. Nissan’s warranty covers defects and capacity loss below 9 bars out of 12 on the dashboard for 8 years/100,000 miles. Hyundai offers one of the longest EV battery warranties at 10 years/100,000 miles with minimum 70% capacity.

It’s important to note that normal battery degradation is not covered under the warranty. Lithium-ion batteries naturally lose some capacity over time and use. This gradual loss is normal and expected. The warranty kicks in if degradation exceeds the rate specified by the automaker.

Overall, EV battery warranties provide important protection against premature battery failure. With warranties spanning 8-10 years, most drivers should not have to worry about expensive battery repairs or replacements during the normal ownership period. However, some basic battery care and maintenance is still recommended to maximize battery life and capacity.

Cost Savings

Charging an electric vehicle at home costs significantly less than fueling a gas-powered car. The average cost to charge an EV is around $0.17 per kWh. With the average EV battery size around 60-80 kWh, a full charge costs $10-14. Compare that to the average cost of a gallon of gas at $3.50. The average new gas car gets around 25 mpg, meaning it costs around $14 to drive 100 miles. An EV can drive that same distance for around $4-5.

Charging overnight also takes advantage of lower electricity rates, further reducing costs. Many utilities offer special EV charging rates well below the national average. Smart chargers that optimize charging times can also help maximize savings.

Overall, driving on electricity costs about half as much per mile compared to gas vehicles. For drivers covering 12,000 miles per year, an EV can save $600 or more annually in fuel costs. The more you drive, the more you save by going electric.

Recommendations

When it comes to charging your electric vehicle battery to 80% or 90%, there are a few key factors to consider:

  • Range – Charging to 90% will give you more driving range between charges. This can be useful for longer trips or if you don’t have easy access to charging throughout the day. However, for daily driving and commuting, 80% is usually sufficient.
  • Battery life – Repeatedly charging to 100% and discharging to empty will degrade an EV battery faster over time. Charging to 80% is generally considered better for battery longevity, as keeping the charge between 20-80% puts less strain on the battery.
  • Cost savings – Charging to a lower state of charge like 80% costs less electricity and can save money, especially when charging at home with time-of-use rates. The extra 20% from 80 to 100% is the most expensive electricity.
  • Public charging – When using public fast chargers, it’s best not to charge past 80% unless you really need the extra range. This helps avoid monopolizing the charger and increases availability for other drivers.
  • Home charging – For home charging, 80% is recommended for most people’s daily needs. But occasionally charging to 90% or 100% before longer trips can be beneficial.

Overall, for most daily driving, charging an EV battery to 80% offers a good balance of range, battery life, cost savings, and charging etiquette. But flexibility is key – charge to 90-100% when you need the extra range, and less when you don’t. Check your owner’s manual for any specific charging recommendations from the manufacturer.

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