Electric vehicle batteries Q&A


Electric vehicle batteries Q&A

On August 18, Plug In America held a webinar looking at various aspects related to electric vehicle batteries, including charging best practices, battery mining and recycling, and their impacts on the electrical grid. There were so many questions asked that we couldn’t get to them all during the live presentation, so below are answers to many of your questions.

Charging Best Practices
Are many small charges better for battery than a few larger charges?

Generally, this is the case. A deep discharge cycle constitutes a full chemical reversal inside the cell, whereas a shallow cycle is not a complete utilization of the chemical resources in the cell.

Do charging cycles intrinsically reduce life?

Every charging / discharge cycle affects battery lifetime, but shallow ones don’t impact the battery as heavily.

Does repeated DC fast charging (DCFC) degrade the life of an EV battery?

Repeated DC fast charging to the high end of state of charge (past 80% or so) may accelerate battery degradation. We suggest only using DC fast charging to reach a very high state of charge if needed to reach a destination.

DCFC impacts on batteries are more significant in EVs with fewer battery modules.  Heat is the main cause of battery degradation. DCFC generates considerable heat, and distributing it evenly over the entire pack reduces the adverse impact on battery life. This is more easily accomplished in EVs with thousands of battery modules rather than hundreds.

What’s the best charging behavior for extending the life of a battery?  Topping off a little every commute day or using the charge throughout the week and charging up the battery over the weekend?

“Topping off after every little drive” might be excessive, if you have only taken a three-mile trip to a store. We recommend gauging your daily driving and incorporating charging into your daily routine.

Take weather into consideration. During exceptionally cold conditions, try to keep the battery more than half full. Leave it plugged for “shore power” to keep the batteries comfortable in the nighttime cold. We recommend against leaving it to sit in the cold at a low state of charge. Note that EVs vary in their features for battery conditioning in cold temperatures.

Will the battery cells balance effectively if you never charge to 100%? How often should someone balance a battery?

Most drivers don’t get into this nuance, and correctly assume that the battery management system takes care of things for them.

Battery balancing is typically done by the car automatically whenever needed. When things get too far out of balance, the vehicle will report an error and require service. A good design will group cells into modules that are dealt with as a block, using a microprocessor-based battery management system and handling dynamic balancing.

If the extreme limits (0 or 100% state of charge) are generally avoided, the battery management system can handle charge balancing. For more background, you can read Davide Andrea’s book Battery Management Systems for Large Lithium-Ion Battery Packs.

Is 100% charge actually 90% or so on my 2016 Leaf?  Or do I need to unplug it before it is fully charged?

We do not have that data on the 2016 Nissan LEAF. Unlike some other EVs, the LEAF does not have a way for the user to set a charge limit. Manually unplugging it every time it is charging would be onerous, so we suggest charging the vehicle as Nissan expects.

In Winter, are you recommending running AC without heat to dehumidify?


We have a car share program using Chevy Bolts. They are fast charged most of the time and many times they are drained completely. How will this affect battery life?

DC Fast Charging does have an impact, but designers take that into consideration by tapering the rate of applied charge. That’s why the Bolt EV takes 2.5 hours to fill completely. There aren’t enough studies done on that lifetime impact yet; over time, we may learn more.

Meanwhile, try to incorporate slower charging where possible. If your car share program does not allow that, it should not have a severe impact. Manufacturers are learning every day what to do and what not to do. The frequent ‘complete drains’ are more concerning.

Should we leave the battery plugged in all day (always be charging, A-B-C), or should we schedule charging to occur just overnight?

Leaving your battery always plugged in depends on the charging system and the EV model. Some recommend it, to keep the battery thermal management system functioning optimally. If you have time-of-use pricing from your utility, you may wish to schedule charging to take advantage of low rates. In extreme weather, you may also approach things differently.

Bolt users have a “hilltop reserve” setting that limits a “full” charge to 87%.

That’s right. This is one approach to the potential over-charging issue.  When one lives “in the heights,” coming down the hill produces copious energy from the regenerative braking system.  Pumping that into a full battery will potentially overcharge it.  The Battery Management System provides the “hilltop reserve” option for the user to select to preserve their pack.  (In future years, that too may be eliminated as a driver concern, so you can roll down a long grade without worry.)

Is it better for battery health to only charge when I need the miles, or should I charge daily and keep it up to about 80% on a daily basis?

That answer depends on your needs, but we do not expect that either approach would significantly impact long-term battery health.

I thought the goal was to keep the battery between 50-80%. I do that unless I’m going on a long trip. Then I take to 100% the night before. Is that the best policy? Or should I fully charge just before I leave? I have a Chevy Bolt.

The 50-80% number probably comes from past advice regarding lead acid (PbA) packs. A Bolt EV can safely go much lower, down to 10-15% state of charge. We just recommend that you not stress the battery (such as flooring the accelerator) at those low states of charge.

Charging the night before to 100% means it is sitting at “totally full” all night.  That should not be a significant problem for a Bolt.

Again, it depends on if this is done regularly and repeatedly. If you use 40% regularly, shift your fill up level to 80% and use more of the middle of your state-of-charge window.

EVs and the Grid
What about the use of EVs as Home Battery for Solar Energy Storage?

This approach is implemented by Nissan in Japan, where it is known as “LEAF to Home.” EVs have also been used in limited “Vehicle to Grid” configurations in the U.S. and in Europe. This is a technically feasible option for providing grid services or emergency backup power. More generally, timing EV charging to when a home or building’s solar panels are generating electricity is effectively a way to store that solar power for later use, even without the ability to return it from the vehicle to the home.

In most cases, with net metering, storage is not specifically needed to accommodate the levels of solar power currently on the electricity grid. But EVs could provide this capability if that changes. This is a developing story.

With climate change causing more storms, thereby causing more power outages, where do you see the solution to battery charging without house power?

The electricity grid can be “hardened” in many ways for greater storm resiliency. This can include better tree-trimming practices, burying power lines, or developing microgrids. It is not invariably true that climate change must lead to more frequent power outages.

Where power outages do happen, EVs can potentially provide limited backup emergency home power with the correct engineering by automakers. And, with today’s larger battery sizes, EVs can typically can meet a week’s driving needs without charging (especially since, in the aftermath of a hurricane, roads are likely to be blocked anyway).

It is important to note that prolonged power outages also mean neighborhood filling stations are also out of service; no power means no electricity for gas pumps!

We do not consider storm-driven power outages to be a significant barrier to EV adoption. We would suggest charging to “near full” if severe weather threatens.

What is V2G/V1G?

V2G represents “vehicle to grid” which is the inverse of charging your car.  It’s returning the power back to the grid (or home or business) from your stored electrons in your battery.

V1G is “half of” V2G. It is also called “smart charging” and involves providing benefits to the electricity grid by responding to conditions and stopping and starting charging. Power does not actually flow from the vehicle to the grid, but this approach can still help utilities keep the lights on for everybody. “Demand response” is one example of V1G; customers receive a signal from the utility or grid operator at times of peak demand and curtail power use in exchange for a payment.  They do not actually put power back on the grid, just reduce the rate at which they take it off the grid.

Will we have to fight 50 different battles in state public utility commissions to provide fair value for the services that second-life batteries can provide?

Not necessarily. Many grid services are obtained through competitive markets run by the grid operators (Independent System Operators, or ISOs). In some cases, EVs or second-life batteries have participated. The primary difficulty is that these markets were set up with the expectations that a few large power generators or major industrial customers would be the market participants, not tens of thousands of EV chargers each drawing 6 kW. Aggregators are working to resolve these issues, so that many small loads can together compete in those markets to receive the fair value for demand response and other services.  It will be an iterative process in most cases as we learn from each other.

Can one “convert” an EV as a home backup battery, like the new LEAF in japan?

Nissan has developed a system which they have not brought to market in the US for extracting power from their LEAF.  We have seen it in action for 3-4 years in the Silicon Valley EV Rally.  The stumbling blocks are many before they could market such in the US, especially since the interconnection to 240 Volt house mains is not trivial. This would not be a “do it yourself” project and we do not suggest that EV drivers attempt this outside of manufacturer-supported programs.

Resources and References
What does SoC stand for?

State of Charge, full is 100%

Are there references for the great facts in the presentations, or industry journals?

A far-ranging reference would be Battery University.

Many peer-reviewed journals provide in-depth investigation of battery issues. Articles by our speakers can be found in Transportation Research Part D: Transport and Environment,  Environmental Research Letters, Sustainable Materials and Technologies, and Journal of Industrial Ecology. Other relevant technical journals include Journal of Power Sources, Journal of Energy Storage, Journal of the Electrochemical Society, and Applied Energy.

Is there anywhere that we can check how a specific auto manufacturer’s batteries have performed over time?

If you have a car you are interested in, you can go to their user group forums and ask questions.  TeslaMotorsClub.com has a data collection from nearly 800 European drivers with high miles on their cars.  They were all subjected to a rigorous and repeatable charge/discharge regime, and then data collected, plotted and distributed.  The projected time to reach the 80% of original capacity mark on their cars was around 22 years. Similar discussions can be found on forums for the Chevy Bolt and Nissan LEAF, and we expect to see more for other models as their market increases.

What is the lifespan of an EV battery?

There is no single answer to this question. It depends on the usage, the cooling system, and the limits of the EV system.

  • If it is a small battery and often exceeding its recommended limits, it will fail sooner. A smaller battery will need less material, but will also undergo more deep charge/discharge cycles for any given driving pattern, so will likely not last as long.
  • If it is a large battery and you stay within boundaries, you can expect good life. With a larger battery, you can keep it in a more optimal SoC range and thereby ensure that it lasts longer.
Alternative Battery Chemistries
Will we be discussing Zinc-Air and Aluminum-Air battery technology?

Zinc-Air and Aluminum-Air batteries are intriguing research topics. Until these are commercially available from multiple sources, it isn’t useful to spend too much time speculating on their characteristics. Lab successes sometimes get stuck in the lab for years or even decades. Commercial availability is key to an automaker.

Is there hope that carbon-ion battery technology could help address these negative impacts of mining lithium, nickel, and cobalt?

Research continues, but candidates have to show enough reactivity to be useful. Carbon isn’t on the active candidate list at this point.

I read that there is research on building crystals for batteries and for solar panels?  Is that true anywhere in research?

Research is just that. After research comes development, followed by production. Many things need to be ironed out before they can transition. That could be years, or decades away.

Many solar panels do use crystalline silicon, but this technology does not apply to EVs.

Where does Lithium Sulfide fit into this story?

It’s evolving. It hasn’t had the final chapter written. Research continues but no viable commercial products have emerged (yet).

What is the opinion on the future solid-state batteries, graphene batteries and other battery types I heard and read about?  Are they better than Lithium Ion batteries?

Time will tell as research continues.

Battery Mining Impacts and Recycling
Do you think people shouldn’t buy EVs until we address these environmental and social impacts? Or can we drive electric now while advocating for change?

We recommend that you drive electric as much as you can when you drive, because the mining impacts are not unique to EVs. The expanding EV market provides a perfect opportunity to demand more responsible mineral sourcing, which means maximizing recyclability, minimizing toxicity, and employing IRMA certification where new mining must occur.

So, yes, drive electric now while advocating for change.

Are there examples of model ethical sourcing policies and battery manufacturing countries can adopt? I heard that a good one is up for review with the European Commission.

For ethical sourcing, we support the Initiative for Responsible Mining Assurance.

What is the state of lithium battery recycling in the US? My understanding is that we have the capability but it’s not actually being done.

Regulations often drive technological developments. The State of California has an ongoing regulatory process underway under AB 2832 (2018) to bring EV batteries into compliance with the goals of the Rechargeable Battery Recycling Act of 2006, which had only covered nonvehicular batteries.

As an EV advocate, I get asked about the issue of how batteries are made and their environmental impacts. Often, this is used as a cudgel to make us look like hypocrites. What is a one-minute response that we can use?

EV adoption is nascent, which makes this a perfect opportunity to get it right. I support and advocate for recyclability, minimal toxicity, and best practices when new mining must occur. Compared to fossil fuels, and ICEs, EVs have an opportunity to build a better, more responsible supply chain.

You might note that there is a climate imperative to decarbonize transportation by 2050 (at the latest). While transit, walking, biking, urban design, and smart growth can play a major role, analysis does not show that they can eliminate global transportation GHG emissions in that timeframe. EVs are a key part of the solution in getting to zero. Accordingly, EV advocates are leading the way in reducing the impacts of battery production.

How much overlap is there between raw materials in cell phones and computers and EVs? How much is demand driven by transportation as compared to other electronics?

Consumer electronics (such as laptops, cell phones, tablets, and power tools) accounted for a majority of lithium-ion battery demand in 2015, but EVs now account for a majority of such battery demand.

Given the dramatic growth in EVs needed to address the threat of climate change, we expect EVs to be the primary driver of new battery demand. EVs will therefore drive new demand for lithium (and cobalt, for as long as that is used, though automakers are seeking to develop superior cobalt-free batteries).

Are there any “easily digestible” resources we can use for consumer education regarding battery lifecycle analysis?

Cleaner Cars from Cradle to Grave, although from 2015, is an excellent and accessible life-cycle analysis report from the Union of Concerned Scientists. We anticipate that an updated analysis will show even better numbers for EVs due to advances in manufacturing efficiency and a cleaner power grid.

Which product is more difficult to control in regards to metals pollution: EV batteries or PV cells? Putting it another way, is it easier to recycle EV batteries or solar panels?

The state of California is looking at this question and will be putting policies in place during the next few years.  Stay tuned as a whole new industry will spring up surrounding recycling both of these.  Luckily, solar panels last a good long time.  And EV “battery second life” applications are promising, such as providing backup power for homes or businesses during power outages.

I have heard a battery recycler say that as battery longevity increases, it will undercut the market for recycling. You need to have a steady supply in order to produce a steady amount of recycled minerals.

Not all that comes from a battery plant (like Tesla’s Nevada Gigafactory) is usable!  They have a steady reject rate.  They deliver 13 million 18650 Li-ion cells each and every day. The Gigafactory already must employ recycling to reclaim materials from unusable cells.

If the EV market grows at the rate needed to address climate change, then over time, there will be many batteries that need recycling, even with increases in pack longevity and “battery second life.”

How many times can a battery be recycled?

That depends on how old the battery is, its previous use (or abuse), the load it is serving, and the capacity of the battery. There is no single answer. The materials can be refined to a near pure state theoretically an infinite number of times, with cost (in energy and other expenses) being the limiting factor.

With Tesla often considered the leader in the BEV market, have they developed a good system for recycling when their batteries are replaced?

We don’t have much insight into the approaches being used for recovery and reject handling at Tesla’s various operations.

However, JB Straubel, the former Chief Technology Officer at Tesla who was responsible for much of the Roadster and Model S/X battery systems, has now started Redwood Materials as a recycling company focused on Lithium packs. We expect an announcement from Redwood Materials soon.

What is the percentage of consumer electronics use vs EV use for rare earth metals?

The percentage continues to change.  Currently rare earth metals are used in tiny motors (like the motor that makes your cell phone vibrate) and throughout any new car. The tiny motors in cars that use rare earth metals adjust the side-view mirrors, lock doors, and adjust seats. The latest and most efficient EV drive motors also use them, especially the new Model 3 and Model Y from Tesla.  EV batteries (the focus of this webinar) by and large don’t use rare earth series elements.

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