Every month at our service centre in Airdrie, we service hundreds of electric vehicles for their current owners, plus inspect dozens more for potential owners. Many of these good people ask about the vehicle’s battery health — and we can’t blame them. The high voltage battery is by far the most expensive part of every EV, after all. However, true battery health and the corresponding failure risk is not well understood by the driving public. In this article, we’ll explain what “battery health” means, why it’s less of a concern than you might understand, and what you should be worrying about instead.

What battery health means to most people:

When most people discuss an electric vehicle’s battery health, they are referencing a parameter called the state of health. When discussing batteries, “state of health” refers to how much energy storage capacity remains compared to when the battery was new. As you likely already know, lithium batteries lose capacity over time. This happens to your phone, your laptop and unfortunately, your electric car as well. The amount of capacity that has been lost is called degradation. As an example, a battery with 7% degradation would have 93% of its original capacity left.

High voltage battery state of health can be measured with various automotive testing tools and we provide these numbers to clients all the time. It’s nice information to have, but also less important than you may realize. Let us explain.

You will never replace an EV battery because it has lost too much capacity.

Before we start receiving emails from dissenting Nissan Leaf or Kia Soul owners, the statement above refers to modern, liquid-cooled lithium batteries. And it’s true! We have repaired or replaced hundreds of high voltage batteries for clients, but never because of degradation. Why’s that? Modern EV batteries typically lose the first five to ten percent of their capacity fairly quickly, but then the rate of degradation markedly slows after that. The average liquid-cooled battery pack can be expected to retain around 90% of its capacity by 100,000 kilometers, 85% by 200,000 kilometers and most of the time, over 80% by 300,000 kilometers or more. Did you know that the cooler climate here in Alberta is actually easier on lithium batteries than a hot climate is? The worst degradation that we’ve ever measured in our shop was 24% loss on a Tesla with over 500,000 kilometers. This vehicle was almost exclusively Supercharged (DC charged) and often charged to 100% — two actions that most owners know aren’t beneficial to battery health.

Given the significant cost involved, very few Canadian drivers would replace an EV battery because their car achieves 10-15% less range. Similarly, we don’t replace gasoline engines just because they have lost efficiency over time. (At 300,000 kilometers, a well maintained gasoline engine will use 5-10% more fuel than when it was new, and poorly maintained powerplants will be up to 20% less efficient.)

So why has My Garage replaced so many batteries, then? What should EV owners actually worry about?

As discussed above, most modern electric vehicle batteries should provide enough range to be considered acceptable for as long as you own the vehicle. Degradation is a nuisance, but it doesn’t spell the end of your battery pack’s life. Which issues do sometimes necessitate a battery replacement? We’ll break them down below.

Cell Failure

This is the most common reason for battery replacement. If an individual battery cell fails electrically (becomes resistive or shorts), bulges/swells or starts to leak electrolyte, the only repair option offered by most manufacturer’s dealerships or OEM service centres is to replace the entire battery pack. This is sometimes the only option that we can offer as well. However, after years of making unmatched investments in tooling and training, My Garage can repair many EV batteries — with the number of batteries that we support increasing every year. Some battery packs are divided into individual modules that can be replaced separately, and dozens of other internal parts can be replaced as well. Many of these parts are hard to find, but we continue to build a growing inventory of unique internal battery components. Our team is even exploring single-cell replacements on certain high voltage batteries. We explore this in more detail on our battery repair page.

Water Intrusion

Everyone knows that water and electricity don’t mix, and this is certainly true within EV batteries. While some breakdowns due to water intrusion can be repaired if caught early, many will require replacement of the entire pack. How does water get inside an EV battery in the first place? Sometimes it happens because of age: Sealant, gaskets and o-rings can harden or deteriorate over time. In other cases, vents or valves become plugged or stuck with dirt and debris, allowing water inside or inhibiting the battery pack’s ability to vent condensation. Many owners of 10+ year old EVs have hired us to clean, inspect and pressure test their battery pack preventatively, to avoid water intrusion issues.

Isolation Faults

An isolation fault is a short (or unwanted connection) between your EV’s high voltage system and the rest of the vehicle. As might be obvious, this separation is important for safety reasons! Isolation faults can happen all over the vehicle, including inside the battery pack. Water intrusion is a common cause of isolation loss inside the battery, along with internal coolant leaks and other faults. Some internal battery isolation issues are repairable but around 75% of them are not.

What do all three of these issues have in common? They are completely unrelated to battery state of health.

Nobody in Alberta services more electric vehicles than we do and from our experience, a battery’s degradation level is not a predictor of lithium cell failure — a higher state of health does not mean a lower chance of failure. In fact, during 2024 and 2025 we actually saw more cell failures on batteries with low degradation (90% SOH or better) than we did on less “healthy” packs. The probability of experiencing water intrusion or isolation loss is, as you’d expect, also completely independent from the degradation level.

If state of health isn’t a reliable indicator, can you predict (or prevent) battery failure?

For the most part, no. But the detailed answer is a bit more nuanced.

Cell failure due to shorting, common on Tesla vehicles, is often caused by a manufacturing defect. During cell production, fine metal particles can be introduced by machinery wear, ambient contamination, or electrode slitting during manufacturing. The particle may not cause an immediate failure and the cell can pass all testing before leaving the factory, so the problem remains hidden. When the cell is charged and discharged, the electrodes swell and compress around the particle, which can cause it to puncture the separator that normally separates the anode from cathode. It often takes years and hundreds of charge cycles for the fault to show up, completely outside the owner’s control.

Cell failure due to resistance increase can sometimes be exacerbated by driving/charging behavior or environmental factors:

• High SOC storage: Owners who charge to 90–100% and leave the car that way, especially in warmer conditions, are building SEI resistance faster than owners who charge to 70–80%.
• Cold fast charging without preconditioning: Creates dead lithium deposits that contribute to permanent resistance increase.
• Temperature cycling: Constantly driving in and out of a warm garage during cold Calgary winters increases condensation and moisture levels within the battery, which slightly increases failure risk.

The other failures that we discussed earlier, water intrusion and isolation faults, can sometimes be prevented through a battery removal, cleaning and inspection when your vehicle reaches 10+ years old.

How do we define a “healthy” high voltage battery?

For our experienced Technicians, this means going way beyond the state of health measurement. When a client wants the most thorough battery inspection possible, we can use specialized equipment to monitor hundreds of battery health numbers in real time: cell voltage and resistance, current and temperature measurements, insulation (isolation) resistance and more. If it is deemed necessary, we can also remove and visually inspect a battery pack, clean vents and valves, and pressure test the battery for leaks. All of this testing, combined with a history of good charging habits as discussed above, usually ensures a battery that will be trouble-free for years to come.

We deliberately inserted the word “usually” there. That’s because a tiny percentage of lithium batteries, even after the most stringent inspection possible, can still test good today and then fail tomorrow. This is no different than an engine, transmission or any other vehicle component.

When your electric vehicle battery fails, what are your options?

Let’s get something out of the way. Despite all the scary language in this article so far (and all of the fear, uncertainty and doubt that you’ll find online), the chance of experiencing an unrepairable battery failure is very low. In fact, we feel that within 250,000 kilometers, you are less likely to experience an EV battery failure than you are to experience the failure of a modern, turbocharged and direct injected gasoline engine.

But if the unthinkable happens, what do you do? Well, for starters, you call us. As mentioned above, many battery failures are repairable. If yours isn’t and you don’t want to purchase a new battery — here’s an article about what that usually costs — we can often provide a low mileage used battery pack for a fraction of the cost. No matter which option we choose to pursue together, you’ll receive a high quality repair and great service from a caring team that always puts your best interests first.