Expressway Speeds Impact on Battery Life?

[dsr302]

My route to work is 25 miles one way.....20 miles are on the expressway with speed limits of 65 mph and the remaining 5 miles are stop-and-go city streets.

I borrowed a Dealer-Demo and drove in to work (Temp 65 degrees so no A/C or Heat) and decided to drive with traffic....speeds were between 65-70. Upon arriving at work, I noticed that I had consumed 40 miles equivalent of power to go the 25 miles. My return trip home resulted in the same power consumption. I thought I'd ask the question of whether the expressway speeds using this much power daily during the work week will be detrimental in the long term life of the battery? I know that battery discharge rate is one of the factors that can impact the life of the battery but I didn't know if this power consumption was excessive and would degrade the battery over time.

Not unless you drive 97 all the time. Don't worry about it at all.

 

[TEG]

Highway commute is a common use of the LEAF. If that adversely affects the battery life there are going to be a lot of disappointed owners in a few years. My guess is that 60-70MPH flat use is probably not excessively hard on the pack. Perhaps if you were in Germany and did top speed (90+ MPH) on the Autobahn daily it might be an issue. Or if you have a daily steep uphill climb with pedal to the floor. I don't think Nissan has really offered any guidance or warnings in this regard. To some degree the motor power output, acceleration and top speed are all somewhat limited (by design) already to avoid overtaxing the battery too much.

 

[UkrainianKozak]

In my experience I'm consuming actually LESS electricity going 60-70mph on highway than going 25-40 local streets while using heater on the cold day. (my local drive have some hills as well, )
My guess stop-and-go traffic on cold days will have worse effect on battery than steady discharge highway driving (worse, but probably by some ridiculously small margin), and I think the absolute worse for the battery is extreme heat, so if you drive and charge at 130F, that would be the worst conditions for the battery.

And yea, don't bother with Leafs Guessometer.
You'll learn to estimate range by using bars instead of the predicted miles. You will know where you go and how - highway/local/hills or not, the car does not know where you will be going next, it can only predict based on previous trip, and it does not do it very nicely.

 

[surfingslovak]

My guess is that 60-70MPH flat use is probably not excessively hard on the pack. Perhaps if you were in Germany and did top speed (90+ MPH) on the Autobahn daily it might be an issue. Or if you have a daily steep uphill climb with pedal to the floor. I don't think Nissan has really offered any guidance or warnings in this regard. To some degree the motor power output, acceleration and top speed are all somewhat limited (by design) already to avoid overtaxing the battery too much.

Indeed, Tom. If I have the numbers right, going steady 70 mph is close to 1C discharge rate. This means that if you drove at that speed for an hour, you will deplete all the usable energy in your battery. That should translate to about 32 amps per cell, which is considered relatively easy on the battery. The Leaf has robust cells with 33 Ah capacity, and this is something they were designed for.

If you are looking for something to be concerned about, it's the jackrabbit starts at 80 kW and over 100 amps per cell. That's 3C or more, which could affect the battery in the long run. Luckily, jackrabbit starts are something we all have in our control. Or so we think ;-)

 

[kubel]

Check out Tony's range chart here:
http://i565.photobucket.com/albums/ss92/TonyWilliams/Nissan%20LEAF/LEAFrangeChartVersion7e.jpg" onclick="window.open(this.href);return false;

As far as battery longevity, I would be more concerned with charge cycles than I would load on the battery. I don't think it will last nearly as long as a gas engine. Nissan says 10 years, but that's a very generic guesstimate. I've heard 1000-1500 charge cycles, but not from Nissan. If that's so, if your drive to work and back takes you from 100% to turtle, you are looking at around 260 charge cycles per year, or around 4-6 years worth of commuting, which is realistically over 100,000 miles assuming 70 miles per day and 1500 charge cycles.

100,000 miles is not great compared to gas cars since their engines can go over 200,000 miles these days. But the amount of money you save not burning gas with that many miles is probably more than enough to replace the battery pack and still see savings afterwards. Plus, every year, batteries are dropping in price and gas is increasing in price. It makes replacing the battery seem less and less of a big deal.

 

[ebill3]

Plus, every year, batteries are dropping in price and gas is increasing in price. It makes replacing the battery seem less and less of a big deal.

I hope it is true that the cost of batteries continues to fall, and it may be. But, the demand for lithium and batteries will increase, and increase in demand does not normally bode well for price decreases. Sure, other battery technologies will appear, but right now Li seems to be the best bang for the buck.

 

[surfingslovak]

As far as battery longevity, I would be more concerned with charge cycles than I would load on the battery. I don't think it will last nearly as long as a gas engine. Nissan says 10 years, but that's a very generic guesstimate. I've heard 1000-1500 charge cycles, but not from Nissan. If that's so, if your drive to work and back takes you from 100% to turtle, you are looking at around 260 charge cycles per year, or around 4-6 years worth of commuting, which is realistically over 100,000 miles assuming 70 miles per day and 1500 charge cycles.

100,000 miles is not great compared to gas cars since their engines can go over 200,000 miles these days. But the amount of money you save not burning gas with that many miles is probably more than enough to replace the battery pack and still see savings afterwards. Plus, every year, batteries are dropping in price and gas is increasing in price. It makes replacing the battery seem less and less of a big deal.

Yes, cycling will certainly have some effect, but if the early data is any guide, the most important gating factor will be calendar life, not cycling.

Please read this Green Car Reports article about our mileage leader, Steve Marsh. He drove his Leaf 36,000 miles and is reportedly unaware of any capacity loss.

There is a similar article about Tom Moloughney on plugincars.com. He has seen only about 2% annualized average range reduction after 50,000 miles of driving in New Jersey, which is not known for its temperate climate. I believe that the cell chemistry BMW used in the field trial was similar to ours, and the ratio of usable to rated capacity was also similar. There was no battery temperature management system to speak of, and Tom did not try to coddle his battery pack, quite the opposite. The MINI-E did not have quick charging capabilities, but it had a more powerful onboard charger. Tom charged 1.5 times per day on average and he reportedly always charged to full.

It's too early to tell, and it's always good to err on the side of caution, but these reports are good news for Leaf owners. I would not be surprised to hear about a Leaf with 200K on the odometer in the future.

 

[zarwin]

My 25 mile one way commute is EXACTY identicle to the mile. 20 miles interstate > 65 and 5 miles stop and go at< 45.

Just as comparison, On the days I cant charge at work, I consistently get LBW when I am a couple miles from home on the return using an 80% charge. So basically on this commute I go 50 miles on 80% charge and have about 4 left on the GOM. I guess that is normal...

 

[surfingslovak]

My 25 mile one way commute is EXACTY identicle to the mile. 20 miles interstate > 65 and 5 miles stop and go at< 45.

Just as comparison, On the days I cant charge at work, I consistently get LBW when I am a couple miles from home on the return using an 80% charge. So basically on this commute I go 50 miles on 80% charge and have about 4 left on the GOM. I guess that is normal...

Zarwin, the guessometer is not worth paying attention to. At least not literally, which appears to be what you are doing. As you know, when you get the LBW, you have about 18% of your usable energy left. Simple math yields a total range of 65 miles. This assumes that you drove your Leaf until turtle. If this was not enough range, you have two options: slow down on the freeway or charge to 100%.

Going 60 instead of 65 or above will have a disproportionate effect. I'm getting about 3.7 to 3.8 miles/kWh energy economy for your commute. If this was consistent with what you are seeing on your dash, then that's on the low side. I believe that 4.3 would be typical for a comparable commute in the summer, and 10-20% less than that in the winter, depending on heater use.

 

[dsr302]

Thanks all for the responses. As always, this group provides a discussion that not only answers my questions but exceeds that with much appreciated additional info.

 

[surfingslovak]

Thanks all for the responses. As always, this group provides a discussion that not only answers my questions but exceeds that with much appreciated additional info.

Glad to hear that you found the information you were looking for, this is a great community, and we are lucky that it came together as well as it did over the last couple of years.

On a related note, Dave mentioned to me that I miscalculated Zarwin's total range, and he is right. I overlooked that the low battery warning came up at the 48-mile mark, and not at 50. Furthermore, he noticed that I forgot to deduct the charge remaning in the battery when the car reaches turtle mode. We both ran the numbers, and came up with a range of around 60 miles on an 80% charge.

The math behind it is not complicated, but it's not something one would do on the back of a napkin. It might be more helpful to point to Tony's range charthttp://www.mynissanleaf.com/viewtopic.php?p=101293 or the reverse SOC project. I used the latter, and came up with this model for Zarwin's commute. For what it's worth, the implied energy economy is about 3.5 miles/kWh:


Click to open

 

[dsr302]

Thanks, that chart contains a wealth of info.

So it shows that 80% charge can go 60 miles until dead. What speeds is this for and is any climate control used? I'm trying to see how this would correlate to my driving habits/conditions.