Bigger Battery = Longer Warranty

[surfingslovak]

So, let me make sure I understand this. If someone bought a Volt or a Fisker and their daily commute is >= 30 miles, charging the battery requires deep cycles, which shortens the battery life. And the battery life of a Volt/Fisker is 20,000 miles (500 cycles x 40 miles).

That's presumptuous at best. Yes, both the Volt and the Karma will have a smaller battery pack than the 150-mile Model S or perhaps even the Nissan Leaf. However, both manufacturers will cycle the pack conservatively, they would be foolish not to.

Take the Volt for example. Rated pack capacity is about 16 kWh and available capacity is about 10.4 kWh. This means that GM is targeting about 60% DOD. They have reportedly emulated 200K miles in their lab and guarantee that the pack will perform like new for 8 years and 100K miles.

I have to admit that I don't know much about the Karma, but I imagine that it's well-engineered. Yes, a small pack is a bit annoying, and it will limit how far you can go in EV mode. However, it does not necessarily mean that it will die a premature death.

 

[Joel]

That's presumptuous at best. Yes, both the Volt and the Karma will have a smaller battery pack than the 150-mile Model S or perhaps even the Nissan Leaf. However, both manufacturers will cycle the pack conservatively, they would be foolish not to.

Take the Volt for example. Rated pack capacity is about 16 kWh and available capacity is about 10.4 kWh. This means that GM is targeting about 60% DOD. They have reportedly emulated 200K miles in their lab and guarantee that the pack will perform like new for 8 years and 100K miles.

I have to admit that I don't know much about the Karma, but I imagine that it's well-engineered. Yes, a small pack is a bit annoying, and it will limit how far you can go in EV mode. However, it does not necessarily mean that it will die a premature death.

Thanks for the insight. I'm still trying to understand the battery technology.

 

[stopcrazypp]

So, let me make sure I understand this. If someone bought a Volt or a Fisker and their daily commute is >= 30 miles, charging the battery requires deep cycles, which shortens the battery life. And the battery life of a Volt/Fisker is 20,000 miles (500 cycles x 40 miles).

I understand the Volt and Fisker have different battery technologies, but is this basically correct?

The LG Chem batteries the Volt uses lasts 1000+ cycles (not sure of exact number); the Fisker batteries supposedly lasts 7000 cycles (but certainly 1000+ for sure). The 500 cycles I gave only applies to the type of batteries Tesla is using (18650 lithium cobalt).

And remember you have to look at FULL cycles, not partial ones. If you look at partial cycles, you have to add them up (two half cycles are roughly equal to one full cycle, etc). Like surfingslovak says, the 35 mile rating is only using 10.4 kWh of 16 kWh, so it'll go 54 miles on a full charge. If the battery was cycled 0-100%, it'll last 54 miles x 1000+ cycles = 54000+ miles.

Again, since they cycle at a shallower range (and never let the battery get completely full 100% or discharged to 0% in its entire lifetime; while in a BEV you have the option of doing that), it'll last significantly longer than that. And you have to keep in mind the warranty is for the total miles (which includes gas miles) and also the fact, that in a plug-in hybrid the total range is less critical (esp. given even at "end-of-life" the battery still has about 70% capacity).

 

[JRP3]

And remember you have to look at FULL cycles, not partial ones. If you look at partial cycles, you have to add them up (two half cycles are roughly equal to one full cycle, etc).

Actually shallow cycling gives better results than that. One full cycle is far more damaging than two half cycles. For example my LiFePO4 cells are rated for 2000 cycles at 80% DOD but they go to 3000 cycles when cycled to only 70% DOD.

 

[vfx]

... And you have to keep in mind the warranty is for the total miles (which includes gas miles) and also the fact, that in a plug-in hybrid the total range is less critical (esp. given even at "end-of-life" the battery still has about 70% capacity).

These points still sound like a hit to those Volt drivers who are driving 100 percent electric to prove a point.

 

[daniel]

I was told by my advocate that the Roadster is designed to be always plugged in. She said it does not really matter much if I leave it unplugged when I'm going to go out again in a short while, but that as a general rule, the official advice from Tesla is to plug it in whenever I'm at a plug (which for me means whenever the car is in my garage).

I'm reading in this thread some reasons for not always plugging it in, such as the preference for keeping the SoC closer to 70% than 90%. My only choices are 90% (standard mode) or 100% (range or performance mode). I understand that I could set the time of day charging to be at a lower charge level at a given time, but I'm retired and don't have a strict driving schedule. So the limited choices (either 90% or 100%) combined with the recommendation to always plug it in, and the fact that I don't think there's an option for "don't charge," or if there is it would be a nuisance to be always fiddling with it, means that Tesla is really recommending, contrary to some posts above, that I charge it up to 90% every day. (I charge at midnight to be at off-peak time for the grid, even though I don't get a reduced rate. I don't care about the rate. I like using off-peak electricity for the environmental benefit.)

So effectively, Tesla wants me to charge to 90% every night.

I'm really not concerned about battery life. With a 245-mile range, even at 50% of its original range I'll have way more range than I'll ever need. So this is all academic to me, but still very interesting. Maybe Tesla should offer more charge-level options.

 

[stopcrazypp]

Actually shallow cycling gives better results than that. One full cycle is far more damaging than two half cycles. For example my LiFePO4 cells are rated for 2000 cycles at 80% DOD but they go to 3000 cycles when cycled to only 70% DOD.

That's why I said "roughly". It's enough to get a minimum number; how many equivalent full cycles you gain from shallower charges depends on so many other variables that there's no general figure that applies.

It seems in your case at 80%DOD you get about 80% x 2000 = 1600 equivalent full cycles and at 70%DOD you get about 70% x 3000 = 2100 equivalent full cycles. So you gained about 500 equivalent full cycles (31.25%) from that 10% reduction in DOD.

I was told by my advocate that the Roadster is designed to be always plugged in.
...
Maybe Tesla should offer more charge-level options.

I think the idea behind that is that leaving it plugged in allows the battery pack to be continually conditioned (since for most people, their garage will be at higher than room temperature, which isn't good for long term life).

Tesla should allow users to set their own max charge-level (it's just a simple software tweak; I know Thinkpad laptops let you do that). That'll address all concerns. Although, right now even the Leaf has a fixed setting (80%).

And I agree, if you can still live with about 70% of the current range in about 7-10 years (the target Tesla seems to be aiming for in terms of warranty; other manufacturers will have different targets), then all of this talk is pretty academic. The car will address most of the points automatically (Normal Mode and battery conditioning in the Roadster; probably similar or better features in the Model S).

 

[Doug_G]

I asked what charging modes the Model S will have at the factory tour. The answer was, "we haven't decided yet."

 

[JRP3]

My only choices are 90% (standard mode) or 100% (range or performance mode).
So effectively, Tesla wants me to charge to 90% every night.

I think that even at "full charge" Tesla still limits max charge somewhat so you aren't really charging the cells to 100%. That is certainly true of the LEAF.

 

[neroden]

I think the idea behind that is that leaving it plugged in allows the battery pack to be continually conditioned (since for most people, their garage will be at higher than room temperature, which isn't good for long term life).

I think you're right. But you're thinking like a Californian. My garage is always at LESS than room temperature... which again probably means it's better to have the battery pack conditioned, especially in the winter when it may be barely above freezing.

Tesla should allow users to set their own max charge-level (it's just a simple software tweak; I know Thinkpad laptops let you do that). That'll address all concerns. Although, right now even the Leaf has a fixed setting (80%).

Indeed, why not?

And I agree, if you can still live with about 70% of the current range in about 7-10 years (the target Tesla seems to be aiming for in terms of warranty; other manufacturers will have different targets), then all of this talk is pretty academic

Yep, I'm in that situation. I do have some long distance drives but I figure in 7-10 years the charging network will be built out better.

 

[SpicyPaneer]

In the next 10 years we can see the 100% charge battery that they use in China right now. Hopefully we will see them in the X & S in the near future