Ageing, like bills, birthdays, taxes and death, comes to us all.
While the middle two might only apply to us humans, battery packs know all about ageing, slowly losing their ability to store charge over time until one day, they can no-longer be useful in the purpose they were originally planned for. It doesn’t matter if the battery is in a laptop computer, a watch, or an electric car: slowly, inexorably, it will age.
So when I glanced over at the dashboard of my Nissan LEAF on Good Friday as we headed out on a family errand, I knew my car had officially hit middle age: its first capacity bar had switched off.
Moreover, as far as we can tell, it’s the first LEAF in the UK to lose a bar.
The twelve bars of ageing
For some reason, when the engineers who designed the Nissan LEAF were planning its digital dashboard, they decided it would be useful to represent not only the car’s state of charge but how much energy it was capable of storing. No other electric car on the market today displays current battery capacity in such a visible way.
As a battery ages, its ability to store energy slowly diminishes. Brand new, out of the factory, the battery will capable of storing far more charge than it will ten years later. At three years and 21 days old and with nearly 52,800 miles on the clock, my LEAF’s battery can now store about 15 per cent less charge than it could when it was new.
Yet when it’s fully charged, the car is still fully charged. It just doesn’t store as much energy as it once did. Hence the two sets of bars on the right-hand side of every LEAF dash.
The larger, leftmost bars count down the charge in the battery pack, slowly ticking down as you flatten the battery pack between each charge. The smaller, rightmost ones, count down the battery pack’s capability to store charge. The more bars lit, the larger the charge it can hold.
And if the car’s battery pack is capable of holding less charge than it once was, the car’s range will slowly tick down too.
The science of loss
According to those in the know, the twelfth segment of the capacity gauge going out represents a capacity loss of around 15 per cent, meaning my LEAF’s battery pack is now capable of storing about 85 per cent of its original capacity.
Of course, this didn’t happen overnight however. From the day I drove it home, my car’s battery pack has been slowly losing its ability to hold charge. So too has every other electric car on the road today, and frankly, every consumer gadget. It’s why your four-year-old laptop doesn’t run on battery power for more than 30 minutes now when once it managed three whole hours.
The reasons why this loss happens, and the factors that effect it, are the subject of a whole different article. But sufficed to say that, like humans, the more stress you put your battery under, the more quickly it will age.
In the case of an electric car battery pack, this means that extremes of heat will induce premature ageing, along with leaving the battery itself in a very high or very low state of charge for long periods of time. Similarly, draining the battery to the point the car enters emergency low-power mode (called turtle mode by many EV drivers) will advance ageing if you do it too many times.
As a consequence, those in extremely hot parts of the U.S. — many of whom have seen their LEAFs’ battery capacities fall enough to turn off two, three, or even four capacity bars in short order — laugh when I tell them our UK LEAF has lost its first bar after a mammoth 52,800 miles. Some of them reached the same point after just 12,000 miles, their car battery packs baked by the blistering Arizonan sun.
Inevitable, accepted reality
It’s also worth noting here that battery capacity loss isn’t linear. The first ten per cent of capacity is lost pretty quickly, then slows down as the battery pack reaches a lower capacity. Then, when the battery is much, much, much older, it accelerates upward again, until the battery is no good for the purpose it was intended for.
In the case of My LEAF, that should be another ten years or more, by which point I’ll either replace the battery pack with a new, improved chemistry pack… or I’ll have sold the car anyway.
Essentially, the battery pack should, even in my situation, last the lifetime of the car. If it were a petrol car, I’d be looking to buy multiple exhaust systems, expensive engine components and perhaps even fund an engine overhaul in the same time frame.
Suddenly it doesn’t seem so bad.
Battery pack capacity loss is affected by so many variables that it’s extremely difficult to predict when and how battery packs will behave in individual circumstances. Nissan, and many independent groups and academics, have built some truly amazing battery capacity models to try and predict what will happen to a LEAF battery pack at a given mileage and temperature.
My car, thankfully, fits squarely into the centre of each predicted model. It is behaving exactly as Nissan predicted. It fits all normal parameters. I can still easily drive 70 miles on a single charge, about the same as I could when it was new. That is to say, while the battery capacity has dropped, my capabilities as a driver have improved. My car drives the same distance it did when new because I’m a better driver 52,800 miles later.
Am I worried? Not really. My car still does what I ask it of. The only times I’ve been towed have been when a charging network let me down (three times in the first year,) I turned up at a non-existent charging station near empty (telematics fault) and last week, when the rear drivers’ side wheel was impaled by a six-inch nail.
In five weeks — despite having one capacity bar less — I’m still taking my LEAF on an epic cross-Europe adventure for Transport Evolved to cover The WAVE. I’m sure it’ll be great.
Besides, after 52,800 miles, I my car is doing pretty well — electric or otherwise. Don’t you?
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