Importance of Electric Vehicle Battery Health
An EV's battery health, just like the engine health of a vehicle with an internal combustion engine, provides vital information about the vehicle's overall condition. Battery health directly affects the following factors:
- Range: A healthy battery ensures that the vehicle delivers a range close to factory specifications. As battery health decreases, the distance that can be traveled on a full charge also decreases.
- Performance: How much power the battery can provide instantly affects the vehicle's acceleration performance. A degraded battery may not be able to provide sufficient power, especially during sudden accelerations.
- Charging Time: The battery's internal resistance can change with its health. This situation can cause charging times to increase.
- Second-Hand Value: The second-hand value of an electric vehicle largely depends on battery health. A vehicle with a healthy battery can be sold at a higher price.
- Safety: A damaged or severely degraded battery can pose safety risks.
Basic Battery Health Metrics: SOH and SOC
When measuring EV battery health, two basic metrics emerge: State of Health (SOH) and State of Charge (SOC).
State of Charge (SOC) - Charge Status
SOC expresses a battery's current charge level as a percentage. This is similar to a smartphone's or laptop's battery indicator. 100% SOC indicates that the battery is fully charged, while 0% SOC indicates it is completely empty. SOC provides instant information for the driver to understand how much range is left, but does not provide information about the battery's overall health.
State of Health (SOH) - Health Status
SOH expresses the ratio of a battery's current capacity to its original capacity when new as a percentage. For example, if a new battery's capacity is 60 kWh and over time this capacity has dropped to 54 kWh, the battery's SOH value is 90%. SOH is the most important health indicator showing how much the battery has worn out and how much life it has left. Generally, when a battery's SOH value falls below 70-80%, it is accepted that the battery has completed its life and needs to be replaced.
How to Measure Electric Vehicle Battery? Methods and Tools
There are several different methods and tools for measuring EV battery health.
1. On-Board Diagnostics (OBD)
Modern electric vehicles continuously monitor the battery's condition through the battery management system (BMS). This data can be read from the vehicle's OBD-II port using a diagnostic tool (OBD2 scanner). This method is one of the most reliable ways to obtain both SOC and SOH values directly from the BMS.
Required Equipment:
- Professional Diagnostic Tool: Advanced models from brands like Autel, Launch, and Topdon offer special battery diagnostic functions for many EV models. These devices can show not only SOH and SOC, but also the voltage, temperature, and internal resistance of each battery cell. This is very valuable for detecting imbalances or potential problems in the battery pack.
- Mobile Applications and Bluetooth Adapters: Special applications such as Leaf Spy (for Nissan Leaf), Dr. Prius (for Toyota hybrids), when used with an appropriate Bluetooth OBD2 adapter, can provide detailed information about battery health.
2. Capacity Test
This method involves applying a controlled charge and discharge cycle to measure the battery's actual capacity. This is one of the most accurate SOH measurement methods, but can be time-consuming.
Steps:
1. Fully charge the battery (100% SOC).
2. Use the vehicle at a constant speed or on a dynamometer until the battery is completely discharged (close to 0% SOC).
3. Record the total amount of energy consumed (in kWh) during this process.
4. Calculate the SOH value by comparing this measured capacity with the battery's original factory capacity.
This test is generally performed by professional services using special equipment.
3. Internal Resistance Measurement
A battery's internal resistance increases as it ages and its chemical structure degrades. High internal resistance reduces the battery's power supply capacity and causes it to heat up more during charging. Professional battery analyzers can measure internal resistance by applying a small AC current to the battery. This value provides an important clue about the battery's overall health. Internal resistance measurement is generally used in conjunction with other diagnostic methods.
4. Load Test
This test measures how well the battery can maintain its voltage under a specific load. A healthy battery keeps its voltage relatively stable under load, while a degraded battery's voltage drops rapidly. This test is useful for evaluating the battery's instant power supply capacity (performance). Load testing is generally done with special battery test devices.
Factors Affecting Battery Health
There are many factors that affect the life and health of an EV battery:
- Charging Habits: Continuously charging the battery to 100% or allowing it to discharge completely can shorten battery life. Generally, keeping the battery between 20% and 80% is healthiest.
- Fast Charging (DC Fast Charging): Fast charging can negatively affect battery life when used frequently, as it causes the battery to heat up more. AC slow charging should be preferred whenever possible.
- Temperature: Extreme hot or cold weather conditions negatively affect battery chemistry. Parking vehicles in the shade or in a closed garage whenever possible is beneficial.
- Driving Style: Aggressive driving and sudden accelerations cause more power to be drawn from the battery, leading to more strain and heating of the battery.
- Time: Like all lithium-ion batteries, EV batteries also degrade chemically over time (calendar aging), even if they are not used.
Conclusion
Measuring the battery of electric vehicles is a vital process for understanding the vehicle's long-term health, performance, and value. Understanding basic metrics such as SOH (State of Health) and SOC (State of Charge) is the first step in evaluating battery health. For the most reliable and comprehensive results, the most effective method is to obtain data from the vehicle's OBD port using professional diagnostic tools from brands like Autel or Launch. These devices offer the opportunity to detect potential problems at an early stage by analyzing not only the overall SOH value but also the condition of each cell. Remember, with proper maintenance and smart usage habits, you can significantly extend the life of your electric vehicle's battery.