Are you shopping for a used car? For decades, the first reflex of any savvy buyer was to take a glance at the odometer. Fewer miles meant a better deal. But today, with the booming market of used electric vehicles (EVs) — driven by the end of the first major leasing cycles — the rules of the game have changed.
For an EV, mileage is no longer the ultimate gauge. The supreme indicator dictating value, lifespan, and your peace of mind is the SOH, or the “State of Health” of the battery.
Here's everything you need to know to buy your next used electric vehicle with confidence.
What exactly is the SOH (State of Health)?
Imagine the SOH as the health report of your car. It is a percentage indicating the energy capacity the battery can still hold compared to its new state (which is 100%).
On average, the industry estimates that a battery loses about 2% of its capacity per year. Practically speaking, a five-year-old vehicle should show an SOH around 90%. However, this figure is just an average! The actual health of the battery hugely depends on how the previous owner treated the vehicle.
Why does a battery degrade?
The drop in capacity isn't due to some dark magic, but rather normal wear and tear. It's caused by two main factors:
Calendar aging: It's the weight of the years. The chronological age of the chemical components and prolonged exposure to extreme temperatures (like our harsh winters or heat waves) naturally wear down the battery, even if the car is driven infrequently.
Cyclical aging: This corresponds to the physical usage of the battery. The number of recharge cycles, the tendency to completely drain the battery (depth of discharge), and especially the frequent and repeated use of ultra-fast charging stations, deplete the internal chemistry more rapidly.
The hidden cost: The importance of vigilance
Why such a focus on SOH? Because replacing an out-of-warranty battery is extremely expensive.
Currently, the replacement cost is around $140 per kWh. To give you an idea, replacing a small 52 kWh battery would cost you more than $8,100. It's therefore crucial to know exactly what you are buying to avoid unpleasant surprises.
Transparency: The new buzzword for dealerships
Fortunately, the market is adapting to protect consumers. In Quebec, pioneers and specialized dealerships, like JN Auto, understand that transparency is vital. They inspect and publicly display the SOH of their entire used inventory, adjusting the sale price accordingly.
To read this renowned SOH, professionals don’t resort to guesswork. They connect directly to the car’s “brain” through the diagnostic port (OBD2). Using AI-powered software, they analyze the data in real-time.
Tools like My Battery Health cross-reference these data with manufacturers' databases.
Applications like La Belle Batterie go further by generating a formal and independent health certificate, super convenient for resale.
The Nissan Leaf example: A display pioneer
Some manufacturers historically tried to make this data visible to the driver. The Nissan Leaf is the most famous example with its dashboard displaying 12 small capacity bars.
The loss of the first bar means the SOH has dropped below 85% (a 15% degradation).
Each subsequent bar disappears with every 6.25% degradation.
Although this system is somewhat rudimentary, it has had the merit of educating a whole generation of electromobilists. Today, purists go even further by connecting an OBD2 reader paired with the LeafSpy Pro app on their phone to get a surgical reading of their SOH, precise to 0.1%.
Pro tips for your purchase
If you are about to buy a used EV, demand a battery health certificate. It's your consumer right, and it's the only way to guarantee the value of your investment.
A not only good SOH secures your purchase, but it also allows you to fully enjoy your vehicle for years while taking advantage (if applicable) of the still available government subsidies for recent used electric vehicles (typically 1 to 4 years old). Drive connected, but drive informed!