Are BEVs Taking Risks to Show Longer Range?

There are different LiON chemistries and battery management systems.

Bob Wilson

 

"some" is your operative word. If your warranty meets your threshold of risk? you're good. If you want a huge battery buffer? You can get that too. We got choices.
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There you go. Threshold of risk.

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One day after my death.

Bob Wilson

 

i'm a warranty guy, more interested in degradation during the life of the warranty. that being said, i would prefer a bev with enough range that i'm not constantly running it down to zero.

 

Which is the prudent way to look at BEV ranges.

There is also the issue of whether the manufacturer is quoting the packs total capacity, or just what the usable portion is.

 

How far is the liquor store where you buy your rot-gut ....

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wegmans, 14 miles round trip, black box cabernet, 3 litres, $16.

 

This is one of the reasons I am benchmarking our BMW i3-REX: Why the BMW i3-REx | Page 16 | PriusChat

Too often I've read automotive press reports that give the rated traction battery capacity instead of the usable capacity and poorly sourced metrics. The window sticker EPA numbers are usable but too often lack details embedded in other, later sources that only an engineer would love. Places that led me to generating these charts BEFORE buying our BMW i3-REX:

Confirmed with:

I have not found similar charts although the data is embedded in the EPA benchmarks.

I have read reports of hot-climate, Leaf owners reporting issues with battery life. But we also had a Gen-1 bought in 2005 and confirmed the mechanisms for Prius NiMH battery degradation in heat and recovery approaches. Owners are the ultimate, last, integration and test team but we need technical ones to do the heavy lifting and figure out how these things really work 'in the field.'

If our owner's manual had the same sort of performance charts found in every light aircraft, I would be perfectly happy. Instead we get data points, better than nothing, but not the type of details needed to really know the car performance.

So let us say there is a standard way to measure the traction battery, usable capacity, from 0%-100% in the usable range. But to run the test stresses the battery taking 0.1% of the remaining capacity (i.e., 1,000 tests leave an unusable battery) and $250 per test, who would elect to run this test over some schedule to track their battery degradation?

Right now, I don't know of a non-destruct, traction battery test that lay people can run. There may be something built-in to cars that I don't own. There may be ways of measuring internal battery resistance (the Gen-1 and Gen-3 Prius do) that can help BUT we know it is not predictive of a failure.

Don't be discouraged but step back from the problem and propose a test, a way that lay people can measure the current traction battery capacity of their ride. In our Gen-1 Prius days, the lay approach was to climb a tall hill in reverse. The altitude reached can be converted into kWh, a traction battery metric.

Bob Wilson

ps. I hate discussing problems that morph into a business plan.

 

Most 'notable' when it comes to traction packs' total versus usable percentage is Tesla's latest 75kWh model S. It's available as a 60kWh that simply widens the unusable portion. You loose ~ 40 miles range, but the benefits are multi faceted. You (at least potentially) greater longevity via smaller use of just the middle, AND, my favorite - the larger unusable portion means no supercharger throttle-back as it approaches its limited 60kWh fill. And it still has a 220+ range epa. ymmv. Sweet!
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is it cheaper for tesla to do it that way?

 

I suppose they think the buyers will eventually get an over the air update to release use to the full 75kEh pack. But they charge $5K less for the 60kWh configuration. I should have mentioned that that's another positive aspect.
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when you say 'eventually get, do you mean pay for? is 220+ miles less than the bolt?

 

It's probably about the same, but of course the bolt won't be able to do 0 to 60 in 4 seconds or less

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true, but if sports car enthusiasts are the only people willing to commit to ev, we're in a world of hurt. don't let your personal desires impede progress.

 

It begs the question: if you ask to to back down to 75kWh, can you get a $5k refund? <GRINS>

Bob Wilson

 

Somewhat.
This is one less battery pack size Tesla has to manufacture.
It streamlines the production lines and simplifies the logistics.

There are also a number of people who are simply hesitant. All the numbers may tell them 220 miles will be sufficient, but the ability to get an over the air software upgrade to increase the range can be reassuring.

To the original question, we have seen no signs of manufactures taking undue risks.

GM, for example, was incredibly conservative with the Volt's battery pack. They only allowed about 2/3rds of the pack to be used.
As they learned, they increased the amount of the pack that could be used.

Combine that learning over billions of electric miles with improvements in battery chemistry and battery management systems and manufacturers are getting more comfortable using more and more of the battery packs.

As for strain on the battery packs, the Volt owners I know have seen no range degradation.
The rate of loss in Teslas have been low, and have not increased over time.
And Leafs have had the exact opposite experience. The first ones had horrendously bad degradation. Nissan learned and improved their battery chemistry as well as management (although still passive) and their battery degradation issues have improved remarkedly.

So no, I don't think manufactures are taking any risks beyond those normally taken introducing new technology into the market.