I’m becoming more optimistic about EV battery longevity. Research shows batteries rarely fail, and most of what I’ve seen has convinced me that battery degradation is not a major concern over the typical lifespan of a vehicle. But Out Of Spec’s testing on this 250,000-mile Tesla Model S is tempering my expectations. First, we saw that the car doesn’t go nearly as far as it once did. Now, we’re seeing that it takes much longer to charge, too.
Ryan from Out Of Spec did a full 0-100% charging test on a high-mileage, 2019 Tesla Model S standard range. And boy, did it take a while. Going from fully flat to fully charged took a whopping 2 hours and 41 minutes. That sounds awful. But don’t give up on high-mileage EVs just yet, as the nuanced version is a lot less dire than the top-line number.
Well over half of that time was just spent getting the Model S from 80-100%. If you know about batteries, that shouldn’t surprise you. They take far longer to fill the closer they get to 100%, as free electrons struggle to find open spaces in the battery to park themselves. That process gets harder as batteries degrade, and harder still if the battery is not properly calibrated and balanced.
That, in fact, explains most of the last hour of charging. Ryan reports that the car’s Battery Management System was off, and had to recalibrate itself and balance the cells. That makes sense: These systems eventually need to be rebalanced, and while many do it automatically, it can only happen under certain conditions. I don’t think the last 10% of this charging curve would be this bad if the test was repeated, though it would still likely be plenty slow.
We never recommend charging to 100% for this reason. That’s why charge times are typically quoted as 10-80% time. That represents the meat of your battery’s charging curve, and what you’re likely to use on road trips and the like. The Tesla Model S charged from 10-80% in about 47 minutes, which really isn’t too terrible. I can’t find what the rate was when new, as this wasn’t a popular model. But while 47 minutes is bad, it’s in the realm of a Chevy Bolt or similar, and since this car was purchased for around $10,000 after factoring in the used vehicle tax credit, that ain’t too shabby.
Its peak rate of 131 kW is also quite solid for the age, even if it tapers quickly. That means a car like this would be better off for frequent, short stops at a low state of charge than 45 minute stops. That’s generally the best road trip strategy in an EV anyway.
Still, it’s not a great performance. I’m still hopeful that most packs will fare better than this, as we’ve seen far higher-mileage Teslas with less degradation. Plus, batteries are improving every year, and today’s units are likely more robust than the base-model Model S’ pack from six years ago. But it’s a reminder that reliability beyond 200,000 miles is never guaranteed. Just ask my 25-year-old 230,000-mile gas truck, which has already needed a new transmission, new radiator, new coolant lines, new transmission and countless other little things. It’s a cruel world out there, and it isn’t nice to cars.
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