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Comment by rgbrenner | Hacker News Reader

Tesla used to (still does?) put larger batteries in their cars than ordered, and limits them with software:

http://www.thedrive.com/sheetmetal/12820/tesla-is-silently-p...

So if these numbers are from the owners reading them from the dash... they wouldn't know their 40kwh battery was actually a 60kwh battery that was software limited. That's a lot of spare capacity to hide aging.

Remember when they flipped a switch to allow Florida owners to use the range of their larger batteries to escape the hurricane:

https://techcrunch.com/2017/09/09/tesla-flips-a-switch-to-in...

Larger batteries than purchased are clearly quite widespread with Tesla.

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The S40 (Model S 40 KWh) was discontinued very quickly, probably no more than a couple thousand ever sold. The only other time Tesla has sold software limited batteries was when they were selling the 60 kWh models with 75 kWh software limited batteries. This only lasted for a few months between the time they started using 75 kWh batteries and when they discontinued the 60 kWh model, maybe another ~20k.

Tesla has sold around 300k Model S and Model X vehicles, so the vast majority are not software limited.

Not saying it's impossible - or even unlikely - but has anyone actually done a tear-down confirming there are identical batteries in cars sold as having different batteries?

The reason I ask is a lot of lithium cell suppliers say "This is an x kWh battery... but don't charge above 90% or discharge below 20%" so the usable capacity is 70% of the advertised capacity. Could be that Tesla just advertises the usable capacity.

Hmm, I think it's not relevant because those constraints apply on the cell level, and Tesla battery packs are just thousands of small cells.

Well I suppose it depends if you leave x% of cells unused (prolonging their life, and ready to swap in when other cells lose capacity, much like SSDs do) or distribute across all cells, lowering the charging level X%. Either way I suspect you're hitting the "full cycle" that diminishes the cells life, so probably better to use the former strategy, leaving you with some healthy cells in the future.

Curious to hear if someone suspects otherwise though.

They don't have cell-level control, so it's definitely the latter. The cells are wired in strings, then paralleled.

http://qnovo.blogspot.co.uk/2014/11/31.html

(although apparently they do have individual fuses!)

Jason Hughes has done some battery teardowns. He actually powers his house with solar and an array of Model S battery packs. The guy's a bit nuts with the EE.

http://skie.net/skynet/projects/tesla/view_post/20_Pics+and+...

Then why does range falls in the first 50k miles, but it slows down after that? If that was a big part of the equation, it would be other way around: range being totally stable for first few years while 'invisible' part of battery degrades, then starting to fall off the cliff.

If you want to go full tin-foil, maybe they drop the range early to help sell the deception.

The 60kWh models with 75kWh battery packs were only sold for a brief period of time, I think their logic was that it cost less to produce a single battery pack for both the 60 and 75. They were identical with the exception of the software limit.

The capacity of all Tesla batteries is larger than the stated one primarily to hit their battery life span targets people who took them apart during salvage report about 15-20% potential higher capacity. It’s essentially the same overprovisioning we do with hard drives and SSDs.

Here is the EPA filing for the Tesla Model S 60 which shows a 65.9kw/h and a 95.5kw/h for the 85/85D. (based on the filing date of 2013..)

https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=31841&...

These are dyno load tests (on the battery) not the actual road/drive tests which are used for the final classification of the car this one is used for the classification of the power train only.

As other people have noted in this discussion, the curve of battery capacity over time does not jive with an overprovisioning strategy.

Both HDDs and SDDs show no almost no degradation until they suddenly have a ton of degradation. (I've owned 3,000 SDDs, 15,000 HDDs, and 1 Model S.)

It doesn’t jolt with their EPA filings which indicate higher capacity for each model time and time again I’ve linked to one from 2013 below and it’s the same story every time.

The degradation pattern is ofc different because SSDs or HDDs are essentially binary the sector or cell is either good or bad and when you go out of spare sectors you are screwed.

Also most of them have many other modes of failure which do not involve their primary capacity.

The Volt behaves in a similar way to protect against degradation, by design. I wonder if the 90% tesla s claim holds for their largest capacity cars as well.

What claim? Every Tesla suggests that you only charge to 90%, no matter how large the battery.

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