Is Tesla’s battery-capacity deal the new standard?

-December 04, 2017

It’s not a secret but apparently it is not a well-known fact, either: Tesla, Inc. sells the exact same car with two different battery ratings and prices (Figure 1). This received some attention as Hurricane Irma was hitting Florida in September, and some owners “suddenly” got an extra 30-50 miles of range, thus enabling them to drive a little further away from the storm’s path.


Figure 1 The Model S (here, the 2013 model) is the most common of the all-electric vehicles from Tesla, Inc (Reference 1).

How did this happen? It’s not by using a different battery pack (Figures 2 and 3). Instead, an article in The Guardian notes that “Tesla’s cheaper models, introduced last year, have the same 75KwH battery as its more costly cars, but software limits it to 80% of range. Owners can otherwise buy an upgrade for several thousands of dollars. And because Tesla’s software updates are online, the company can make the changes with the flick of a virtual switch.”


Figure 2 The Model S battery-pack assembly is relatively flat and positioned under the car, stretching across the car’s width and for most of the length (Reference 1).


Figure 3 A high-level diagram shows the main high-voltage electrical components of the Model S (Reference 2).

This practice of deliberate “downgrading” is not a new development, of course. It’s been done since the early days of modern electronic hardware, where a hidden jumper or internal switch allowed the same production product to run with more speed, resolution, memory, or some other tradeoff. In some cases, there were even discussion groups that told customers the secret, so they could upgrade it on their own (although that would void the warranty).

With the advent of software upgrades, the vendor and user situation became much easier. Many applications came with all their modules already installed but enabled only when the user entered a vendor-supplied code (upon payment, in most cases). Still, the decision to actually enable functions and features was done only with deliberate action by the customer.

Now, though, with the pervasiveness of the Internet and connectivity in almost every device, the vendor can access the product and enable or disable features or install upgrades remotely, and may not even need to check with the user (Microsoft Windows 10 installs updates when it thinks you need them, so the next time you use your PC, something may have changed that affects your work or work style).

However, I don’t recall any comparable situation where basic battery capacity could be adjusted remotely. While it may make BOM and production sense, it still bothers me that all users have to pay for the entire battery assembly, and also the weight penalty of the unusable cells. That’s a real and tangible burden beyond just reducing the available kW-hr that the pack can supply.
 
I also wonder how the battery and power-management engineering team must feel (not that their feelings are a factor). No doubt they worked long and hard to develop and evaluate batteries, controllers, and algorithms to maximize the battery pack’s useable capacity, life, performance, and other factors. Then they find that “marketing” has decided to cut off about 10-20% of that capacity, solely to offer different capacity ratings at different price points. That’s got to hurt, at least professionally.

I’m not taking a position on whether Tesla should or shouldn’t do this. As long as the buyer gets the range promised, I suppose all is well. Still, I do worry that this kind of intimate battery management, beyond doing what has to be done to maximize battery performance, may become a new marketing-upgrade ploy. What’s next: differing levels of battery life in your smartphone, solely at the discretion and control of the vendor? That’s certainly feasible.

What’s your view on this sort of battery-management and downgrade/upgrade tactic?

Bill Schweber is an EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features.


References
  1. What Goes Into A Tesla Model S Battery--And What It May Cost, Green Car Reports
  2. Review: Tesla Motors’ all-electric Model S is fast—but is it a good car?, Ars Technica

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