[joeker]

Ok I drove one over the weekend and totally fell in love with the car. I would appreciate any help. After reading through the post everyone seems to be happy with their Karma. My question is: What's the battery lifespan because I know it's really pricey. Thanks in advance.

 

[Ira]

Ok I drove one over the weekend and totally fell in love with the car. I would appreciate any help. After reading through the post everyone seems to be happy with their Karma. My question is: What's the battery lifespan because I know it's really pricey. Thanks in advance.

There are battery experts on this Forum who can answer that question better than I.

But here's my $.02 worth:

Assuming you get a Karma with the latest battery type (I'm sure someone here will inform you about how to know that), EV batteries can have a lifetime of about 15 years.

You'll know it's time to change the battery when it can no longer take or maintain a full charge. For example, that might be a number like 80% state of charge (SOC).

The other important factor (besides time in service) is the number of charging cycles the battery can accept. Let's use 2000 as an example. (Does anyone out there know what the number of cycles is?) Anyway, using 2000, if you recharge your Karma every day, it would begin to fail after 5.5 years. However, there's a catch: If you partially charge it every day (we call it "topping it off"), that's not counted as a cycle. You can control how deeply you discharge the battery by using the Sport Mode. A big plus of having a hybrid.

Another factor is operating temperature. The warmer the operating temperature, the shorter the range and the battery life. Although the cooling system in the Karma keeps the battery pack well-below the 140 degree failure temperature, I wouldn't drive around in the desert during the heat of the summer, just in case the cooling system fails.

 

[Ira]

There are battery experts on this Forum who can answer that question better than I.

But here's my $.02 worth:

Assuming you get a Karma with the latest battery type (I'm sure someone here will inform you about how to know that), EV batteries can have a lifetime of about 15 years.

You'll know it's time to change the battery when it can no longer take or maintain a full charge. For example, that might be a number like 80% state of charge (SOC).

The other important factor (besides time in service) is the number of charging cycles the battery can accept. Let's use 2000 as an example. (Does anyone out there know what the number of cycles is?) Anyway, using 2000, if you recharge your Karma every day, it would begin to fail after 5.5 years. However, there's a catch: If you partially charge it every day (we call it "topping it off"), that's not counted as a cycle. You can control how deeply you discharge the battery by using the Sport Mode. A big plus of having a hybrid.

Another factor is operating temperature. The warmer the operating temperature, the shorter the range and the battery life. Although the cooling system in the Karma keeps the battery pack well-below the 140 degree failure temperature, I wouldn't drive around in the desert during the heat of the summer, just in case the cooling system fails.

I just found this Website, which talks about optimum SOC among other things:

http://www.designnews.com/document....84,industry_auto,aid_261882&dfpLayout=article

 

[joeker]

Thanks guys

 

[non sequitur]

I just found this Website, which talks about optimum SOC among other things:

http://www.designnews.com/document....84,industry_auto,aid_261882&dfpLayout=article

From Ira's link: "Other factors also play into the life expectancy of lithium-ion batteries. The first of those factors -- temperature -- is the most important. Batteries that are exposed to high mean temperatures tend to degrade significantly faster than those in colder climates. “If you’re living in Abu Dhabi, the battery life will be much shorter than if you’re in a place that has colder winters,” Cugnet told us. “And if you have your car parked under the sun in Atlanta or Louisiana three months of every year, the battery won’t last 20 years.”

Wow - what a contradiction from the expose in the NYT about the now infamous Tesla road trip, where it came to light that electrics perform better on a single charge in a warmer climate than the cold NE in winter. So better on a single charge in the heat, but lifespan diminished - everybody loses.

Also from the link (this is the relevant part to this thread):
The wrong charging techniques can also shorten a battery’s life. Lithium-ion battery packs need to stay as close as possible to a 50 percent charge, he said, usually going no higher than 80 percent and no lower than 20 percent. Moreover, electric car owners should refrain from doing too many “fast charges,” in which an EV battery can be recharged in under an hour.

More bad news for Tesla - in this case, their supercharger network.

 

[SoCalGuy]

Also from the link (this is the relevant part to this thread):
The wrong charging techniques can also shorten a battery’s life. Lithium-ion battery packs need to stay as close as possible to a 50 percent charge, he said, usually going no higher than 80 percent and no lower than 20 percent. Moreover, electric car owners should refrain from doing too many “fast charges,” in which an EV battery can be recharged in under an hour.

This is why I usually store my Karmas with around 21 miles or so of electric range (which is approximately 50% charge for the battery).

 

[dennis]

The wrong charging techniques can also shorten a battery’s life. Lithium-ion battery packs need to stay as close as possible to a 50 percent charge, he said, usually going no higher than 80 percent and no lower than 20 percent. Moreover, electric car owners should refrain from doing too many “fast charges,” in which an EV battery can be recharged in under an hour.

More bad news for Tesla - in this case, their supercharger network.

The superchargers are spaced approximately 100 miles apart so typically you don't need to do a full charge to reach the next one. Also, charging has to be slowed down as the battery gets full so you don't want to take the extra time to charge the Model S to full capacity at a supercharger. In 10 months/6000 miles I've only done a full charge 5 times, and never at a supercharger.

 

[Ira]

Should We Switch to Sport Mode at 20% SOC?

This is why I usually store my Karmas with around 21 miles or so of electric range (which is approximately 50% charge for the battery).

For more on this subject, see:
http://www.lacarguy.com/green/article/eight-tips-to-extend-battery-life-of-your-electric-car

Anyway, this thread and the above article got me to thinking about ways to increase battery life. The batteries are so expensive, that even adding a few years would save a lot money. For example, if I have to replace my battery in 8 years, I should set aside $2.5K per year in a Karma battery fund. But if I can increase that interval to 12 years, then the annual battery cost drops to $1.6K. (Batteries will be cheaper in the future, but the logic of keeping the original battery longer before it becomes a boat anchor remains the same.)

For those of you interested in the science, Google on Electric Vehicle Battery Technologies - Springer, which discusses the factors affecting EV batteries life. I was particularly interested in the DOD (Depth of Discharge) discussion and it's affect on battery life, because that's one of the few things we can control using Sport Mode. So rather than allowing the Stealth miles go to zero, why not switch to Sport at 10 miles or 20% SOC? It might cost a couple of bucks in gas, but wouldn't that be negligible in the overall scheme of things?

I'm aware of the 15% reserve for stop and go traffic, but let's face it, when our EV range is 0, we might have deeply-discharged the battery and therefore reduced it's life-cycle.

 

[Fabulist]

For more on this subject, see:
http://www.lacarguy.com/green/article/eight-tips-to-extend-battery-life-of-your-electric-car

Anyway, this thread and the above article got me to thinking about ways to increase battery life. The batteries are so expensive, that even adding a few years would save a lot money. For example, if I have to replace my battery in 8 years, I should set aside $2.5K per year in a Karma battery fund. But if I can increase that interval to 12 years, then the annual battery cost drops to $1.6K. (Batteries will be cheaper in the future, but the logic of keeping the original battery longer before it becomes a boat anchor remains the same.)

For those of you interested in the science, Google on Electric Vehicle Battery Technologies - Springer, which discusses the factors affecting EV batteries life. I was particularly interested in the DOD (Depth of Discharge) discussion and it's affect on battery life, because that's one of the few things we can control using Sport Mode. So rather than allowing the Stealth miles go to zero, why not switch to Sport at 10 miles or 20% SOC? It might cost a couple of bucks in gas, but wouldn't that be negligible in the overall scheme of things?

I'm aware of the 15% reserve for stop and go traffic, but let's face it, when our EV range is 0, we might have deeply-discharged the battery and therefore reduced it's life-cycle.

The 15% reserve is only accessed wth the genset running and it is a very short-term loan. In normal operation, the battery stays very close to 15% charge as the power borrowed from the reserve is almost immediately replaced from the genset. There is nothing wrong with using sport mode manually to manage the SOC, but it seems that the battery management computer is already very conservative and doing what you suggest would further limit EV range without much impact on the battery.

 

[Ira]

The 15% reserve is only accessed wth the genset running and it is a very short-term loan. In normal operation, the battery stays very close to 15% charge as the power borrowed from the reserve is almost immediately replaced from the genset. There is nothing wrong with using sport mode manually to manage the SOC, but it seems that the battery management computer is already very conservative and doing what you suggest would further limit EV range without much impact on the battery.

Thanks for the clarification and technically you're correct as indicated by the discharge curve for a typical lithium-ion cell. But I'm still concerned about operating in that 15% reserve range, which is on the edge or within the deep discharge area, depending on temperature. In that area of the curve, rapid discharge during acceleration followed by rapid recharge by the genset (or braking through regen) is got to be hard on a battery that should ideally (although impractically) be maintained at 50% SOC for max life.

We can call this effect a "knee-jerk reaction."

Also, I've noticed that on a hot day, that last 10-15 miles melts away pretty fast. Do you know why the battery management system does that when the discharge curve should be flatter on warm days? I haven't measured it, but it seems like I'm expending 2 battery miles for every mile traveled. So if I maintain the last 10 miles by using Sport Mode, it's probably only costing 5 miles of gasoline ($1) during the summer and keeping me out of the knee of the curve in the winter.

 

[clsr2nrvna]

Love the graphic Ira! Thanks for helping the visually inclined