Nissan Leaf Battery Replacement

Friday 12th August, 2011
Auto Express are waving around a headline grabbing story that "Leaf battery could cost £19k" drawing some rather questionable comparisons. For example, this replacement price is more than buying a new VW Golf Bluemotion. They also quote Nissan as stating that the battery capacity will be at 80% after five years, dependant upon charging and usage.

So where does that leave Leaf buyers?

Well, in all honesty, exactly where they were before this "news" came to light. There's nothing new here, it's just an attempt to get a few website hits after Top Gear made Leaf bashing fashionable in the media. Those of us who attended the LEAF Press Launch in Lisbon, almost a year ago, were told then of the expected 80% capacity after five years and that this wouldn't be covered by the products warranty - just as loss of horse-power on a traditional ICE vehicle wouldn't be. Rory Reid was one one of the few to cover that at the time, in the "Cost assesment" section of his write-up after the event.
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It was also widely speculated at the time, although admittedly not confirmed by Nissan in the briefing, that Li-ion cells like those in the Leaf had a list price of around £500 per kWh - pricing that in the Leaf to around £12k. Assuming this is a wholesale price, add on an approx. 50% margin and we're in the ballpark suggested by Auto Express.

Of course, as was touched on in the AE piece, the Leaf isn't just one big lump of battery that needs to be replaced in one go - it's a series of cells that click together a bit like lego bricks.  You can make the batteries as big or small as you like,  each module (lego brick) holds 500Wh of charge and to reach the quoted 24kWh capacity we need 48 of them. In reality, I'm led to believe (that means it's not 100% confirmed), Nissan threw in a few extra bricks taking the true capacity of the battery up to 28kWh - that's 8 spare modules.

Having spare cells in the battery has two benefits. The first, obvious one, is that the battery still has full capacity if some were to die prematurely. Components like this are often measured using an MTBF (mean time between failure) and, whilst the average life-time may be many years, there will be some that die very young and some that live to be old - a bit like humans have an MTBF of say 60 yrs, We don't all die on our 60th Birthday and some die very young. Nissan will know the MTBF of their battery components, and the range around it, and spec accordingly. The second benefit is that, by using the extra capacity and a bit of clever battery management, they can extend the life of the battery. Instead of having to fully charge 48 cells each time you plug it in, instead you can charge the 56 cells to around 85% - this significantly reduces wear on components.
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So let's analyse the story a bit closer. Nissan say that the capacity may be 80% after five years - e.g. by this time they expect many of the cells to have died. We know that they already threw in a few extra for good measure, so for total available charge to be 80% of 24KWh (19.2kWh) then we have likely lost 28-19.2=8.8kWh of cells. We'll call that 18 x 500Wh modules.

From the Auto Express article we know these apparently cost £404 each so 18 x £404 = £7272 - so the cost to refurbish the average Leaf battery, to new condition, after 5 years is around £7000, hmm...isn't that what Top Gear said?

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