When To Charge An EV Battery?

When to Charge EV Battery

Navigating the world of electric vehicles (EVs) can be a challenge, especially when it comes to maintaining battery health.

This article is here to guide you through this journey, offering practical solutions to common queries about optimal charging practices. Leveraging extensive research and industry knowledge, we’ve compiled informed recommendations tailored to all EV owners and enthusiasts.

We’ve broken down complex concepts into accessible language, making it easy for everyone to understand.

Just like you, we’re passionate about sustainable transportation and are committed to helping you get the most out of your EV experience.

At a Glance:
1️⃣ EV batteries are robust, and the car’s battery management system provides most of the needed protections.

2️⃣ Despite this, you must never discharge below 10 – 20% (manufacturer dependent)

3️⃣ To prevent battery damage, never store the vehicle 1ith less than 20% charge or more than 80% charge.

When To Charge Your EV Battery?

Choosing the correct charging time is one of the best EV charging practices you will become familiar with. After understanding when to charge, you might also want to know how long it takes to charge an electric car.

Optimal Charging Times 

The optimal charging times are as follows:

  • Charge the car when it is not needed for a while (overnight)
  • Charge the car when electricity prices are the lowest.
  • Charge the car when the temperature is approximately 70F (21.5C)

Factors Affecting Charging Decisions 

The factors that affect when you charge your EV battery are as follows, and these are related to how much it costs to charge an electric car.

When You Need The EV

If you don’t need the car until the next day, overnight charging is the optimal solution. If you are traveling and need to recharge quickly, using a charging station with a fast charger is the most efficient scenario.

Charging During Off-Peak Hours

To ensure that you operate cost-effectively the optimum recharging time is overnight in off-peak cost cycles. If you’re using solar power, knowing when to charge your EV battery aligns with understanding the best time to charge with solar.

Effect Of Charging Habits On Battery Health

You should rarely charge your Electric Vehicle battery to 100% for several reasons.

The Speed Of Charging

EV battery charging does not happen in a linear (straight) line. The higher the battery’s state of charge, the slower it absorbs energy.

Beyond 80% charge, the charging rate slows down significantly, and, particularly if you have a queue of cars waiting to use the public charger, it becomes very inefficient to complete the charge.

As you are already paying for using the charger, the cost of the charge becomes uneconomic.

The Battery’s Health

There is a commonly held belief that EV batteries should not be charged to more than 80% to preserve long-term battery health. 

While many support the 80%/20% notion, a body of research is being developed which demonstrates that a 100% state of charge has no material impact on the battery.

The advice from EV manufacturers also varies. There is general agreement that if an EV battery is left at 100% charge, the long-term battery life will become compromised.

Depth Of Discharge

EV batteries are generally Lithium-ion or the slightly updated LiFePo units. Neither of these technologies performs well below 15- 20% depth of discharge (DOD). Knowing when to charge can help prevent your electric car from sitting too long without charging.

If either of these battery types is discharged below the DOD levels, the long-term health of the unit will be compromised.

Knowing when to charge can help prevent your electric car from sitting too long without charging. Learn more about how long an electric car can sit without charging.

Temperature Considerations 

All batteries, including EVs, are designed to operate within an optimal temperature band of 70oF (21.5oC) is the vehicle the optimum temperature.

Cold and high temperatures affect the rate and efficiency of the battery’s chemical reactions. This applies to the charging as well as the charging modes.

Heat Has A Detrimental Impact On EV Batteries

The hotter a battery gets, the faster the reactions take place. This means that the “wanted” reactions needed for discharging and recharging, and unwanted reactions (that reduce the long-term battery life) happen faster.

The unwanted reaction happens when high heat impacts the protective SEI’s composition and organization (the anode’s surface layer.) The heat causes reactions and causes two issues:

  • It uses up active lithium.
  • It creates inert compounds on the anode that prevent the ions from flowing freely.

Charging a battery in high heat effectively increases the force that moves the ions across different nodes. If the temperature is too high, the battery may suffer stress fractures and damage to the nodes.

Cold Also Has A Detrimental Impact On EV Batteries

While cold weather will generally not reduce the battery life (above freezing), it will make it less efficient in the short term. This results in the following issues.

Longer Charging Times – The cold reduces the energy for ions to move within the battery. By slowing the ions down, charging times are increased in colder weather.

Reduced Battery Range – The primary reason the Battery Range of EVs is reduced in cold weather is that the car’s auxiliary heating and cooling are used. 

Unlike Internal Combustion Engine Cars (ICE), the battery powers the car’s systems, including the motors and the auxiliary systems. 

In cold weather, the battery power is used to heat the cabin and the vehicle’s battery. When the heating systems in the car are turned on, they increase the battery’s discharge rate. 

Avoiding Overcharging

We have already touched on the question of overcharging a battery. In reality, this is almost impossible with modern EVs as the vehicle’s Battery Management System (BMS) will control the amount of charge that is actually accepted by the vehicle.

EV manufacturers offer a range of advice that varies from always charging the battery to 100% to never doing so.

The two schools of thought are researched at the following links:

  1. 80/20 rule is not relevant – Source
  2. 80/20 rule is correct and applicable – Source

Maximizing EV Battery Life

You can take some practical measures to ensure you get the maximum EV battery life.

Monitoring Battery Health

An Electric Car battery is not as simple to look after as a conventional lead-acid unit found in ICE cars. 

For the most part, they are not easy (near impossible) to access, and secondly, the DC power they provide could be deadly if not handled properly.

Because of this, the best way to maintain battery health is to keep the battery operating within the parameters set by the manufacturer. 

Use the onboard computer to monitor the battery’s health. If indicated, take it to an authorized dealer to check it out.

Reduce The Number Of Times The Battery Is Charged

The number of charge/discharge cycles available measures rechargeable battery life expectancy. Manufacturers generally provide two limits:

  • The number of charging cycles available until the battery drops to 80% capacity.
  • The total number of charging cycles that can be expected.  

Therefore, limiting the frequency of recharge cycles lowers battery degradation.

  • Don’t speed – While using the torque unique to EVs is fun, unfortunately, the range is reduced, and the battery will need to be charged more often.
  • Avoid Driving in icy conditions – It is not always possible, but if you can avoid going out in frigid weather, you will need to charge the EV battery less often.
  • Don’t overuse DC fast charge systems – These systems produce heat which harms the battery’s life expectancy.

Store The EV Under the Correct Conditions

Research agrees that batteries should be stored with the battery charge being less than 80% and more than 20%. 

Key Takeaways

1️⃣ Optimal practices for charging electric vehicle (EV) batteries include charging when they are not in use, during low electricity cost periods, and at around 70oF (21.5oC) temperature.

2️⃣ Discharging the battery below 10-20% and storing the vehicle with less than 20% or more than 80% charge should be avoided to prevent battery damage.

3️⃣ Charging habits can affect battery health. Charging beyond 80% slows down the charging rate and could potentially impact long-term battery life.

4️⃣ Temperature plays a significant role, with both high and low temperatures affecting the battery’s efficiency.

5️⃣ Emphasis is placed on the importance of monitoring battery health and reducing the frequency of recharge cycles to maximize battery life.