Does the performance degrade with battery age?

jhs_7645 · Aug 6, 2012

Since it seems that 0-60 times are tied to the output of the battery (40kWh == 6.5, 60kWh==5.9, 85kWh= 5.6), I'm wondering if the performance (0-60 times) degrade as the battery's max range capacity decreases over time?

The reason I ask is to help me with my decision regarding performance version v. non-performance version. I plan on having this car for a long time, and nothing I've seen says that the inverter can be upgraded later. Also, as larger battery packs come out in the future, assuming they will be offered as replacement batteries, will that also affect performance?

AndyM · Aug 6, 2012

jhs_7645 said:
Since it seems that 0-60 times are tied to the output of the battery (40kWh == 6.5, 60kWh==5.9, 85kWh= 5.6), I'm wondering if the performance (0-60 times) degrade as the battery's max range capacity decreases over time?

The reason I ask is to help me with my decision regarding performance version v. non-performance version. I plan on having this car for a long time, and nothing I've seen says that the inverter can be upgraded later. Also, as larger battery packs come out in the future, assuming they will be offered as replacement batteries, will that also affect performance?

My assumption would be no. The battery isn't the different component in the Performance model, its the inverter. I would expect the range, not the current pulled from the battery, to degrade over time.

jhs_7645 · Aug 6, 2012

AndyM said:
My assumption would be no. The battery isn't the different component in the Performance model, its the inverter. I would expect the range, not the current pulled from the battery, to degrade over time.

How would that explain the disparity among the other versions? Do they all have different inverters? Is that an assumption, or something that we know to be true?

ggr · Aug 6, 2012

There is a limit to how much current you can pull from each cell. The smaller batteries have either less, or smaller, cells, therefore you can not draw as much current from the battery as a whole. To a very close approximation, the current you can draw at a particular voltage won't change very much until the cell(s) start to really degrade. The difference between the normal and performance versions of the 85kWh models seems to be a beefier inverter, I think the inverter for all the non-performance models is the same.

jerry33 · Aug 6, 2012

jhs_7645 said:
How would that explain the disparity among the other versions? Do they all have different inverters? Is that an assumption, or something that we know to be true?

My understanding is that the inverter pulls a given maximum amount of current from each cell (each sheet actually). The more cells there are in a battery the more current the inverter can pull. Because the voltage of the individual cells remains constant throughout the useful life the cell, the maximum amount of power the inverter is able to draw remains more-or-less constant. So the number of cells dictate the amount of power that the inverter can draw (up to the maximum allowed by the inverter).

AndyM · Aug 6, 2012

jerry33 said:
My understanding is that the inverter pulls a given maximum amount of current from each cell (each sheet actually). The more cells there are in a battery the more current the inverter can pull. Because the voltage of the individual cells remains constant throughout the useful life the cell, the maximum amount of power the inverter is able to draw remains more-or-less constant. So the number of cells dictate the amount of power that the inverter can draw (up to the maximum allowed by the inverter).

Which would explain the varying 0-60 times:

4.4 perf, 5.6 non-perf (85kWH), 5.9 (60kWh), 6.5 (40kWh)

jhs_7645 · Aug 6, 2012

jerry33 said:
My understanding is that the inverter pulls a given maximum amount of current from each cell (each sheet actually). The more cells there are in a battery the more current the inverter can pull. Because the voltage of the individual cells remains constant throughout the useful life the cell, the maximum amount of power the inverter is able to draw remains more-or-less constant. So the number of cells dictate the amount of power that the inverter can draw (up to the maximum allowed by the inverter).

Interesting... it would be nice to have that confirmed, are there any roadster owners with degraded batteries that can comment?

jhs_7645 · Aug 6, 2012

One more note (not to drag this out) is from Tesla's FAQ:

How long do the batteries last?

The battery pack in your Tesla Roadster is expected to maintain good driving performance for about 100,000 miles or five years, whichever comes first. Lithium-ion batteries will degrade slightly over time. Our testing and modeling indicate that a typical Tesla Roadster owner who drives 50,000 miles over five years should have about 70 percent of initial performance levels available.

Note that it says 70 percent of initial performance levels...

jerry33 · Aug 6, 2012

The European Roadster owner who recently passed 200,000 km indicated that about 70% of his range remained--my understanding is that he races his Roadster regularly so his is a worst-case scenario. Because he was racing when he passed the 200,000 km mark I really doubt his performance was down 30%.

VolkerP · Aug 7, 2012

Cell degradation increases internal resistance. This will increase voltage sag. Example: when drawing 1200A, pack voltage will drop from 400V to no just 330V but to 270V. This will reduce power output.

Doug_G · Aug 7, 2012

VolkerP said:
Cell degradation increases internal resistance. This will increase voltage sag. Example: when drawing 1200A, pack voltage will drop from 400V to no just 330V but to 270V. This will reduce power output.

When a Roadster gets down to 50% charge you don't see a significant drop in performance. The electronics can draw a bit more current to make up for the drop in voltage - within limits of course. Obviously if you're trying to do drag racing the pack should be pretty full, but I'd doubt you could tell the difference without instrumentation.

I doubt you'll see significant performance loss until the battery gets below 70% capacity.

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