5 Ways to Minimize Range Loss in Fleet Electric Cars

 In EV Charging

Degradation of lithium ion batteries over time is a common problem for all portable electronics users. Each time a battery cell is charged or discharged it loses a little bit of capacity. When battery loss affects laptops or cell phones, it’s a minor annoyance that usually won’t cost much to fix.

When an electric vehicle loses energy storage capacity, it could eventually render the car unusable without a costly replacement pack—which will typically set you back $5,000 or more.

The rate of capacity loss a battery undergoes varies significantly depending on a number of factors, especially:

  • Vehicle model and pack design
  • Battery Chemistry
  • Climate
  • Charging habits
  • Time and usage

In extreme cases, some Nissan LEAF owners have experienced significant battery loss just months after purchasing their vehicles. Others have managed negligible losses after thousands of charge cycles in the same vehicle. One taxi fleet in the UK put more than 100,000 miles on a LEAF in less than 22 months—under a grueling charge schedule—but lost less than 13 percent capacity.

Minimizing battery loss in fleet plug-in vehicles requires planning, which ideally begins before selecting a model for purchase. Understanding why range loss occurs and how to mitigate it can save you money on maintenance costs, prolong the usable life of the car and increase its resale value.

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What Is Electric Vehicle Range Loss?

There are two kinds of battery degradation: calendar capacity loss and cycling capacity loss. As its name suggests, calendar loss occurs over time as a battery is left holding a charge. The higher the state of charge (SOC) and the longer it remains stored, the more degradation occurs. Temperature is also a major—and often most important— factor in calendar loss, as we’ll address later.

Cycling capacity loss results from charging and discharging the cell, which affects the structural integrity of graphite particles in the anode. Degradation from cycling is a function of both the total number of discharges and how extreme they are. Bringing a battery from a 100% SOC to 0% will cause maximum cycling loss.

How to Prevent Range Loss

In truth, concerns about battery degradation and range loss tend to be overblown. Carmakers plan for these factors and design their vehicles to resist them to the greatest extent possible. These five rules of thumb will have different impacts on different vehicles depending upon design.

Nevertheless, it’s important to research each plug-in model in your fleet and understand your charging and usage patterns in order to keep your batteries in the best condition possible.

1. Avoid High Temperatures

The single most important factor in preserving the life of a lithium ion battery is heat. In cities where temperatures regularly near 100 degrees, EV owners need to be particularly cautious selecting and taking care of their cars. A number of Nissan LEAF buyers in the Southwest United States learned this back in 2012 when their cars began to experience significant range loss due to heat.

Lithium Manganese Battery Calendar Life

Via ElectricVehicleWiki.com

In the above graph from ElectricVehicleWiki.com we see how long it takes lithium manganese batteries to lose 30 percent of capacity at different temperatures. This shouldn’t be taken as a prediction for the rate of range loss plug-ins will experience.

Unlike many consumer electronics, most plug-in vehicles have sophisticated battery management features to mitigate these effects. Still, the graph helps to illustrate just how important temperature can be to battery life.

Does this mean that EVs should be avoided in warmer climates? No. But if you’re planning to introduce an EV into your fleet in Phoenix, you should probably avoid parking it in direct sunlight at a high SOC during the day.

2. Fully Charged Cars Are For Driving, Not Parking

As a general rule, lithium ion cells last longer when they’re kept between 20-60% SOC as much as possible. This means different things for different plug-in models. The Chevy Volt, for instance, always reserves some of its battery in either direction—meaning that it’s never fully depleted or fully charged. As such, Volts rarely experience noticeable range loss.

From a practical standpoint, the best step a fleet manager can take to avoid battery loss stemming from SOC is to time charging around usage.

Most plug-in vehicle models and charging stations allow you to control charge times to take advantage of off-peak utility rates. The closer you can time charging to the period where the vehicle will actually be driven, the less calendar capacity loss you’ll see. For low-mileage vehicles that rarely push the upper limits of their range, it may make sense to set charging to stop at 60 percent of capacity or lower.

For most vehicles, it’s extremely important to never leave the battery fully discharged for long periods of time. In some cases, leaving a battery empty for too long can “brick” the car, meaning that it’s pack will have to be replaced.

The less time a vehicle spends at either extreme of the spectrum the better.

3. Don’t Use Quick Charging Unless Necessary

High-voltage direct current charging can quickly recharge a typical EV to about an 80% SOC in under an hour. The downside is that some vehicles can experience significant range loss when regularly connected to a fast-charger. This is mostly due to the additional heat that is created by the quick-charge process compared to a Level 1 or Level 2 charging station.

When the Nissan LEAF first hit the market, Nissan executives warned that using the optional quick charge capability on a daily basis could increase capacity loss at a rate of roughly 1 percent per year. Not all plug-ins will necessarily suffer from quick-charging though. Tesla says range loss from using its Supercharger network—if it even exists—is negligible.

BMW i3 Thermal Management

BMW uses a special air conditioning system to keep the i3’s battery pack cool.

4. Select the Right Models

Each carmaker’s vehicle and battery designs are unique. Be it cell chemistry, thermal management systems or charging control software, the solutions manufacturers employ to protect batteries have varying levels of effectiveness. If your fleet is located in a hot weather climate, it’s important to select a plug-in with an active thermal management system. Rather than simply cycling air through the pack—as Nissan does in its LEAF—an active cooling system uses refrigerants to powerfully reduce battery temperature. Based on real world performance thus far, vehicles from Tesla, BMW, GM, and Ford appear to fare much better in warmer climates thanks to active cooling.

Another thing to consider is the total range of a car itself. Opting for a vehicle with more range than you’ll need on a regular basis gives you the option of charging to a lower state of charge each night, which extends battery life. You’ll also want to ensure that your fleet has the capability to time and control charge cycles in order to avoid leaving cars sitting at a high SOC when not in use.

5. Use Telematics to Manage Battery Health

Preserving the range of plug-ins comes down to knowing your vehicle, how it’s used, and creating a plan to minimize practices that could lead to battery degradation. Telematics allow fleet managers to know how their vehicles are being used and even monitor the current health of a pack and how much range has already been lost. It won’t always be possible to avoid heat, quick charging, or the other factors we’ve covered here, but solidifying a strategy to mitigate them will prolong the life of your battery pack and save money in the long term.

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  • canuckinthewild

    Very useful article, Zach. One quibble is that I don’t quite agree with your definition of an “active” TMS. Air cooling can be done both passively and actively. The Leaf TMS (such as it is) is passive, while the i-MiEV and Soul EV have active air cooling. Liquid cooling is, of course, always active.