EV Battery Health
14Dec, 23 December 14, 2023
  • By evcharger

A key component of any EV is its battery, which stores the energy that powers the electric motor. As EV batteries age and degrade over time, it’s important for owners to understand what impacts battery health in order to maximize lifespan. This article will provide a comprehensive overview of the factors that affect EV battery health, with a focus on charging habits, frequency, and methods.

How Do EV Batteries Work?

Lithium-ion batteries are the dominant battery chemistry used in modern EVs. They have a higher energy density, lower self-discharge, and lower maintenance requirements compared to other rechargeable battery types.

The cathode is typically made of lithium metal oxide, while the anode is graphite. During charging, lithium ions are released from the cathode, flow through the electrolyte, and insert themselves into the graphite anode, while electrons flow through an external circuit. This stores energy electrochemically.

During discharging to power the motor, the lithium ions flow back to the cathode, releasing electrons to the external circuit, which provides the power. Hundreds of thousands of small lithium-ion cells are combined into modules and packs with monitoring systems to form a complete EV battery.

Moreover, battery management systems monitor temperature, charge levels, and other parameters to optimize performance and safety. Newer solid-state batteries aim to replace liquid electrolytes with solid compounds to improve stability. Recycling lithium-ion batteries to recover materials is also an important consideration.

Factors That Impact Battery Health:

There are several key factors that can affect the long-term health and degradation of EV batteries:

Temperature

Exposure to excessive heat is one of the most detrimental influences on battery health. High temperatures cause accelerated chemical breakdown within the battery. Studies have found that EVs operated in hot climates above 90°F may experience significantly faster battery degradation over time. 

The chemical reactions powering the battery can become unstable at elevated temperatures. Automakers actively cool batteries during charging when possible to mitigate heat-related wear. Maintaining a moderate temperature range improves battery life.

State of Charge

Storing the battery at very high or very low states of charge for prolonged periods actively degrades it. Keeping the charge level at around 50% is optimal as it places less stress on battery components. 

The active materials strain less at moderate charge levels than at maximum full or minimum empty states. Owners can maximize battery life by not allowing it to sit fully charged or depleted for extended durations when not in use.

Charge Cycles

Although each charge/discharge represents one cycle that slowly damages the battery structure, EVs are engineered for thousands of routine charge cycles over ten or more years of service. 

Fast Charging

Frequent use of fast DC chargers can cause more rapid performance loss compared to slower Level 2 charging at home each night. The battery must work harder and heat up more during quick, high-voltage charging sessions. Minimizing reliance on fast chargers by planning trips with ample at-home charging time in between extends battery longevity.

Vehicle Use

Simply driving the electric vehicle on a regular basis does little to deteriorate the battery on its own. Routine cycling through discharge and recharge is how the battery is designed to function without accelerated wear. Similarly, higher long-term mileage alone does not necessarily degrade batteries more quickly than sitting idle, unlike combustion engine vehicles.

How Charging Impacts Battery Health?

Charging habits and methods can have a significant impact on the degradation of EV batteries over time. Here is a detailed look at how different charging factors affect battery health.

Charging Frequency

Frequent shallow charges are better for battery health compared to sporadic deep discharges. Keeping the battery between 20-80% charge is ideal. However, leaving the battery at a high state of charge at all times accelerates degradation.

The best practice is to charge on a routine daily charge to 80%, with periodic full discharges. Avoid leaving the battery near full or empty for extended periods.

Charging Levels

Level 1 (120V) vs. Level 2 (240V): Higher voltage Level 2 charging is faster but causes slightly more degradation over time compared to lower Level 1 charging. However, the difference is small over the life of the battery.

Level 2 charging is recommended for routine daily use to optimize charging speed and battery health. Use Level 1 for maintenance charging if time permits.

AC vs. DC Fast Charging

DC fast charging provides the fastest but is harsher on batteries compared to AC charging. Minimize the use of DC fast charging. It should be used for travel when necessary, not daily charging.

For daily use, stick to AC Level 1 or Level 2 charging whenever possible to maximize battery lifespan. Some automakers limit fast charging or warn about battery degradation after excessive sessions. Follow manufacturer guidelines.

Charging Power Level

  • Many new EVs allow adjustable charge current/power levels (e.g., 5kW, 7kW, 10kW).
  • Higher power levels charge faster but produce more heat and strain. Lower power levels are gentler on the battery over time.
  • Use the lowest power level that provides sufficient charge speed for your needs. Only use max power occasionally when time is limited.

Charging to 100%

  •  Most automakers recommend limiting the maximum state of charge to 80-90% for daily use.
  • Charging to 100% causes strain and accelerates capacity loss over time.
  • Charge to 100% only when needed before a longer trip. Otherwise, limit to 80-90% for daily charging.

Battery Health Management Systems

Modern EV batteries have sophisticated battery management systems (BMS) that help prolong battery life:

  • Monitors cell voltages and temperatures to prevent damage.
  • Controls charge and discharge rates within safe limits.
  • Balances cell voltages during charging.
  • The thermal management system cools the battery to prevent overheating.

However, the BMS cannot overcome the effects of excessive heat, fast charging, or leaving the battery at high/low charge for too long. Following the proper charging practices is still important to maximize battery lifespan despite the safeguards.

Signs of EV Battery Degradation

There are a few key signs to see if your EV battery is degrading:

  •  Reduced driving range – Vehicle doesn’t go as far per charge
  •  Longer charging times – It takes longer to recharge the battery
  •  Loss of power – Sluggish acceleration
  •  Battery capacity loss – Lower capacity reported by the battery management system
  •  Error messages – Battery-related warning lights or errors

Well-maintained EV batteries will see gradual capacity loss of around 2-3% per year, or 20-30% over the vehicle lifetime. Faster degradation may indicate an underlying issue.

Battery Lifespan and Replacement

  • EV batteries are expected to last at least ten years and 100,000 miles, if not longer.

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  • Nissan LEAF batteries have been known to degrade more quickly in hot climates. Tesla batteries maintain higher capacities for longer.
  • When capacity drops below 70-80%, the battery may need replacement. Warranties typically cover up to 8 years.
  • Battery replacement costs $5,000-$10,000+ depending on vehicle model and warranty status.
  • Some automakers like Nissan remanufacture and reuse EV batteries for energy storage systems after vehicle use.

Battery Chemistry Differences

  • EV batteries use lithium-ion chemistry, but there are several types (NMC, NCA, LFP, etc.) with different characteristics.
  • NMC and NCA have higher energy density but may degrade faster than LFP batteries, which tolerate more abuse. Tesla uses NCA, while many others use NMC.
  • Chemistry differences account for some variability in degradation rates between EV brands/models.

Battery Chemistry Differences

  • EV batteries use lithium-ion chemistry, but there are several types (NMC, NCA, LFP, etc.) with different characteristics.
  • NMC and NCA have higher energy density but may degrade faster than LFP batteries which tolerate more abuse. Tesla uses NCA, while many others use NMC.
  • Chemistry differences account for some variability in degradation rates between EV brands/models.

EV Battery Chemistries

ChemistryCommon ModelsAdvantagesDisadvantages
NMCNissan Leaf, BMW i3High energy density, widely available.Can degrade faster in heat.
NCATeslaVery high energy density.Expensive, needs careful thermal management.
LFPChevy Bolt, HyundaiLong cycle life.Lower energy density.

Tips for Maximizing Battery Health

Here are some best practices for maximizing EV battery lifespan:

  • Avoid exposing the vehicle to high temperatures whenever possible. Park in the shade or garage.
  • Charge daily to around 80% to avoid staying near full or empty for too long.
  • Use lower-power Level 1 or Level 2 charging for daily charging when possible.
  • Minimize the use of DC fast charging for occasional travel needs rather than daily charging.
  • If adjustable, use lower amperage charge settings to reduce strain on the battery.
  • Let battery discharge to 20-30% before recharging to “recalibrate” periodically.
  • Limit maximum charge to 80-90% for daily use. Only charge to 100% when needed.
  • If storing for long periods, maintain around 50% charge and recharge monthly.

Following the proper charging habits and avoiding excessive heat exposure will go a long way toward preserving your EV’s battery capacity and lifespan. Be sure to follow the charging recommendations in your vehicle’s manual as well.

Conclusion

The lithium-ion batteries used in today’s EVs are designed to have long lifespans. However, charging behavior and environmental factors can have a significant impact on battery health and degradation over time. Using the proper charging methods, avoiding heat exposure, and following automaker guidelines will maximize an EV battery’s lifespan. While some capacity loss is inevitable as batteries age, proper maintenance and charging habits can help you get the most out of your EV battery.