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Questioning the battery numbers : article

Questioning the battery numbers : article

NEWS2017 Tesla Model S: Don’t Trust Its Numbers By Allison Blackburn | December 20, 2016 SHARE TWEET SHARE SHARE 0 COMMENTS
It looks like the 2017 Tesla Model S cannot be trusted when it comes to numbers. The carmaker measures the capacity of the battery by the total amount of energy potential of the pack instead of using the total usable capacity to gauge it. The Nissan Leaf for instance offers the 24kWh battery and this has a usable capacity of 21.3kWh.

Tesla does stand out in one aspect and this is using the capacity in branding. For instance, the Tesla Model S 75 has he 75kWh battery in it. Now we have heard details about the actual usable capacity of the battery packs of Tesla and this tells shoppers about bargains and options to avoid.

One owner of a Tesla vehicle revealed a discrepancy first in the battery capacity advertised by the carmaker and the actual capacity. He went through a teardown of the 85 kWh battery that has been discontinued on the Model S. He said that the battery offers a capacity of only 81kWh and the usable capacity is 77kWh.

Now access has been gained to the battery management system of Tesla and tests were made on vehicles that included the Tesla Model X 60D. The battery capacity was said to be 61Kwh while the usable amount was actually 58.5kWh. on the 90D and P90D the battery is 85.8kWh of which 81.8kWh is usable and on the 75 and 75D the battery is 75 kWh and 72.6kWh is available.

The tests also showed that the upgrade to the 75 range wasn’t such a good deal while the Model S60 was a bargain.

But what are your thoughts on the battery of the Tesla vehicles, do they meet your expectations when driving and do figures really matter?

Dramsey | 08/01/2017

I've been completely happy with the range and capacity offered on my P85 and 90D. That said, Tesla does specifically note battery capacity, i.e. "90kWh" on the order page, so a case could be made for false advertising.

Bighorn | 08/01/2017

We've known this for years. People buy range, not kWhs.

TeslaTap.com | 08/01/2017

I'll take a shot at this. Let's keep it simple with the 85 battery and I'll even go with the numbers above. You might get far more than 85 kWh out of the battery, especially if you are willing to drain it to 0% (which Tesla tries very hard to not let you do). This is not 0% indicated SOC (State of charge), but 0% where the battery has zero voltage left. The downside is you really don't want to do this, as the battery may not charge again. This is called bricking the battery (i.e. you end up with a brick). But - truth in advertising, it does have 85 kWh of energy - perhaps more.

Now some will point to a 18650 battery data sheet and claim some numbers. The problem is 18650 is the physical size of a battery size - not some particular cell (it means 18mm diameter, and 65.0mm long). Panasonic and others make a range of 18650 batteries, and Tesla uses a custom formulation that is not publically documented, nor the same as other cells sold for consumer laptops and other goods.

So let's look at usable battery energy - this again could be defined in many different ways. One common way is the power that let's you run the car, also often talked about going from 100% SOC to 0%. This is clearly less than 85 kWh and the 77 kWh quoted above seems valid. But what if you drain it to 0% SOC as indicated on the car's instrument display. Tesla is not draining the battery completely at 0% SOC. It stops providing motor power at 0% indicated SOC, but the battery still has quite a bit of energy left - energy you paid for!

So your car ran out of "power" at 0% SOC - and you left it at the airport for another month without charging after it went to indicated 0% SOC. You really don't want to brick the battery, so Tesla includes a safety buffer. I've seen numbers in the 5-8 kW of safety buffer, but this is really hard to measure without risking the battery. This safety buffer should let the car go at several more months before the battery may be destroyed. So you do pay for this safety buffer to prevent total battery destruction - a feature that was often lacking in early EVs to the dismay of owners that bricked their expensive battery pack.

So the only deception is the article's author having a poor understanding how the battery is rated and how the actual capacity is used, and the need to make a eye catching headline.

drklain | 08/01/2017

Just one other comment, in ICE vehicles there is also fuel tank capacity and usable fuel. Those numbers are not the same thing either. A fuel tank's usable capacity is always less than the overall capacity for a number of reasons (not the least of which is that the tank suction point is not on the bottom of the tank to avoid sucking up any sludge that might be in the tank.

Not saying it is as much as the issue in a BEV, but there is always some amount of capacity you can't use -- even if you are willing to run the battery (or fuel tank) dry (which no normal person does).

SCCRENDO | 08/01/2017

For the 85 battery it was well calculated. There was about 4kW anti-bricking and 7kWh below 0 reserve giving 74kWh below 0

SCCRENDO | 08/01/2017

74kWh useable battery

blue adept | 11/12/2019

Reads like someone somewhat desperately trying to sow the seeds of FUD...again.

Ross1 | 11/12/2019

Its flagged away now.