Why is 90% EV Battery Charge on A Road Trip The Magic Number?

Electric vehicles (EVs) are transforming road trips as we know them. Gone are the days of traditional fuel stops; today’s journeys are powered by electrons. But this new way of travel brings its own set of rules, especially when it comes to managing the power source of EVs: the EV battery. Understanding how to optimally charge your EV can turn a good road trip into a great one.

With EVs, the magic number often isn’t 100% when it comes to EV battery charging. Surprisingly, stopping the charge of your EV battery at 90% can be the key to a smoother, more efficient journey. It’s not just about getting from A to B; it’s about getting there smarter, faster, and with less hassle, that’s what we all want in the end.

Whether you’re a seasoned EV traveller or contemplating your first electric road trip, understanding the workings of EV battery charging is essential.

How do EV Batteries Work

Electric vehicles (EVs) are more than just cars without a conventional fuel tank; at their core lies the EV battery, a complex assembly of cells and electronics that powers everything from the headlights to the acceleration on the motorway.

The Basics of EV Battery Composition

• Cells and Modules: An EV battery is made up of individual cells, grouped into modules. These modules are then assembled to form the battery pack.
• Lithium-Ion Technology: Most EV batteries today use lithium-ion or LFP technology. It’s preferred for its high energy density – meaning more power with less weight.
• Battery Management System (BMS): This integral system monitors and manages the battery’s performance, ensuring safety and longevity. It controls everything from temperature regulation to charge levels.

How EV Batteries Differ From Traditional Fuel Systems

• Energy Storage vs. Energy Production: Unlike petrol or diesel engines which produce energy through combustion, EV batteries store energy. This energy is then used to power an electric motor.
• Instant Torque: EVs deliver torque instantly, thanks to the immediate response of the electric motor powered by the battery. This results in quicker acceleration compared to traditional internal combustion engines.
• Regenerative Braking: A key feature in EVs, where the energy produced during braking is converted back into electrical energy and used to recharge the battery slightly.

The understanding of how EV batteries work is crucial in appreciating why charging strategies, particularly the 90% rule on road trips, are vital. It’s a blend of physics, chemistry, and a bit of smart technology that makes electric road trips not just possible, but increasingly preferable.

Charging Curves and Their Impact

When we talk about charging an EV, it’s not a linear process. The rate at which a battery charges varies, and this variation is best understood through charging curves.

Understanding Charging Curves

• What is a Charging Curve?: Simply put, a charging curve is a graph that shows the charging speed (in kW) of the battery over time. It’s not a straight line but a curve that changes shape as the battery charges.
• The Fast Charge Phase: Initially, when the battery is low, it can accept charge at its maximum rate – this is often the fastest part of the charging process.

Why Batteries Charge Slower Towards Full Capacity

• Battery Protection: As the EV battery charge level increases, the charging speed slows down. This is intentional, designed to protect the battery’s health and longevity. Fast charging generates heat, and too much heat can degrade the battery.
• Chemical Limitations: There’s also a chemical aspect. As the battery gets fuller, the ions that move to store energy have fewer vacant spaces to occupy, slowing down the process.

The Typical EV Battery Charging Curve

• Initial Rapid Charge: The curve typically starts steep, indicating a fast EV battery charge.
• Gradual Decline in Charging Speed: As the EV battery gets around 50-70% full, the curve starts to flatten out, indicating a decrease in charging speed.
• The Tapering Off: Finally, beyond 90%, the curve becomes much flatter, showing a significant reduction in charging speed.

This behaviour of the EV battery charging curve is central to understanding why stopping at an 90% charge can be more efficient on a road trip. While the first 90% can be achieved relatively quickly, the final 10% can take disproportionately longer, making it an inefficient use of time during a journey.

Optimising Charge Times on Road Trips

On a road trip, time is of the essence, and how you manage your EV’s charging can significantly impact your overall journey time. Understanding the efficiency of charging more often, instead of waiting for a full 100% charge, is crucial.

The Efficiency of Frequent Charging

• Time-Saving Strategy: Charging your EV up to 90% and then hitting the road again is often faster than waiting for a full charge. This approach leverages the fast initial charging phase, avoiding the slow charging that occurs as the battery nears full capacity.
• Avoiding Diminishing Returns: After about 90%, the charging rate drops sharply. Spending time charging beyond this point yields less value for the time invested, as the added range per minute of charging drastically decreases.

Real-World Implications for Travel and Planning

• Journey Time: By charging your EV battery more frequently but for shorter durations, you can maintain a higher average speed across your journey, reducing overall travel time.
• Route Planning: This strategy requires a shift in route planning. Drivers need to identify charging stations that fit within their new charging routine, which is where the abundant availability of chargers in the UK comes in handy.
• Charger Availability: Considering the widespread network of charging stations, you’re seldom far from the next charging point. This abundance allows for more flexible planning and less anxiety about running low on charge.
• Battery Health: Frequent, shorter charges are also gentler on the battery, potentially extending its overall lifespan compared to consistently charging it to 100%.

In essence, optimising charge times is not just about saving minutes; it’s about a smarter, more efficient way to approach EV road trips. It’s a strategy that aligns with the unique characteristics of EV charging, turning what might seem like a limitation into an advantage.

Benefits of Stopping at 90% Charge

Adopting the 90% EV battery charging rule of thumb on road trips isn’t just about personal efficiency; it has broader benefits, particularly when it comes to reducing congestion at charging points and making the most of the UK’s extensive charging network.

Tesla already has introduced 90% charging fees in the US on congested charging hubs. It would not surprise us that these kind of measures will be introduced here in the UK.

Reduced Congestion at Charging Points

• Shorter Charging Sessions: By stopping at 90%, charging sessions are shorter. This turnover at charging stations means more drivers can use the facilities in a given period, reducing wait times and congestion.
• Better Utilization of Resources: Faster charging cycles allow more EV drivers to benefit from the existing infrastructure, especially during peak travel times.

Charger Availability in the UK

• Abundant Network: The UK boasts a very reasonable network of EV charging stations, we’re still far behind EU countries like The Netherlands and Germany, but as of my last update, there were thousands of public charging locations across the country, a number that has likely grown already.
• Strategic Placement: Many of these chargers are strategically located along major routes and destinations, making it easier for EV users to rely on frequent, shorter charges.

Comparative Analysis: Charging to 90% vs. 100%

• Time Efficiency: Charging from 0 to 90% can often be accomplished in a relative fraction of the time it takes to go from 90 to 100%. For instance, getting to 90% might take around 30 minutes, while the remaining 10% could take nearly as long.
• Range Anxiety vs. Time Management: While charging your EV battery to 100% might seem like a solution to range anxiety, it’s often an unnecessary precaution given the density of the UK’s charging network. The time saved by stopping at 90% can often outweigh the slightly reduced range.
• Overall Journey Impact: For road trips, the cumulative effect of faster charging sessions can significantly reduce total travel time. This time saved can be better spent enjoying the journey or reaching your destination sooner.

In summary, stopping at 90% charge offers a pragmatic balance between maintaining a healthy battery range and efficient use of time and charging infrastructure. It’s a strategy that not only benefits the individual driver but also contributes to a smoother experience for the wider EV community.

Practical Example: A Road Trip Scenario

To bring the concept to life, let’s consider a practical scenario: a road trip from London to Edinburgh, a journey of approximately 410 miles.

The numbers will be different for every electric car, EV, but the 90% rule of thumb will apply to almost every EV on the road, there will always be some rare exceptions.

The Journey with 90% Charging Strategy

• Vehicle Specs: Assume an EV with a real world motorway range of 250 miles at full charge.
• Starting Point: Fully charged in London, the first leg of the trip is 210 miles, roughly 90% of the car’s range.
• First Charge: Near Nottingham, the EV is charged back up to 90%, a process taking about 40 minutes.
• Second Leg: The journey continues for another 200 miles, requiring a second charge near Newcastle.
• Final Leg: The last stretch to Edinburgh is covered with the remaining charge.

Time and Distance Comparisons

• Charging Time: Each charging session, up to 90%, takes approximately 40 minutes. So, total charging time is about 1 hour.
• Total Journey Time: Including driving and charging, the journey might take around 7 to 8 hours.

The Journey with 100% Charging Strategy for Comparison

• Longer Charging Sessions: Charging to 100% could add an additional 20 to 30 minutes per charge.
• Total Charging Time: This means total charging time could be up to 2 hours.
• Total Journey Time: The overall journey time could increase to around 8 to 9 hours.

Real-World Implications for Travel Efficiency

• Time Savings: By stopping at 90%, you save up to an hour of charging time depending on the car.
• Reduced Stress: Frequent, shorter stops are less taxing than longer waits, especially on longer journeys. You could easily use this time to get a coffee or use the facilities.
• More Time at Destination: Arriving earlier allows for more time spent at the destination, rather than on the road or at charging stations.

This simple example illustrates how, by strategically managing the EV charging process, not only can you make your journey more efficient, but also more enjoyable.

It’s a practical demonstration of how embracing the unique aspects of EV travel can turn a long drive into a smooth and even enjoyable part of your adventure.

Were will this go?

The 90% charging strategy for electric vehicles (EVs) on road trips offers a blend of efficiency, convenience, and foresight. This approach leverages the faster charging rates at lower battery levels and avoids the diminishing returns of topping up to full capacity. It’s a method that mirrors the evolving landscape of EV technology and road trip culture.

Summarising the Benefits

• Time Efficiency: By spending less time charging your EV Battery, more time can be devoted to the journey or the destination.
• Reduced Congestion: Shorter charging times mean quicker turnover at stations, easing congestion.
• Battery Health: Frequent, less intense charges are gentler on the battery, potentially enhancing its lifespan.
• Travel Ease: With the abundance of charging points across the UK, the 90% rule is easy to incorporate into travel plans.

Looking to the Future

The future of road tripping with EVs is bright and promising. As EV battery technology advances and charging infrastructure expands, strategies like the 90% EV battery charge rule will continue to evolve. We are witnessing a big shift in how we travel – a shift towards a more sustainable, efficient, and enjoyable form of transportation.

In embracing these changes, we’re not just adapting to a new type of vehicle; we’re participating in a revolution in travel. One that respects the limits of our planet while expanding our own horizons.

The 90% charging strategy is more than a practical tip; it’s a sign of this new era of road travel – smarter, cleaner, and more attuned to the rhythms of our world and the technology that propels us forward.

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