How should Nissan respond to dropping capacity?

[palmermd]

Then they went on public with the GreenCarReports article and downplayed it like it was just a fluke/anomaly. If that's the case, why wouldn't they be interested to investigate my fluky case further? That's because they already know. And they TOLD ME that THEY KNOW.

I agree with most everything said in this thread and that there appears to be a real problem with heat but the greencareports article is useless as a reference. It is by no means a statement from Nissan. It is an unknown person who claims to be a Nissan employee who made a statement at an unknown point in time.

Nissans silence is not good. They need to make some sort of statement soon even if it is just to say "we are aware and are investigating"

[GerryAZ]

I feel a need to provide at least 1 data point showing that not all Phoenix Leafs are losing significant battery capacity: After 12 months and 11,400 miles, I still have 12 bars and, as far as I can tell, have not lost significant capacity. Since I do not have a Gid meter, my method to keep track of battery capacity has been to record charging energy. I have recorded charging energy from shutdown to 100% several times over the past year and have not seen a significant decrease. My capacity may have started out a bit lower than others have reported, but it has dropped very little over the past year. I need to get the data entered into a suitable spreadsheet to post. I have done things that may be bad for the battery and other things that should be good:

1. Almost every charge is to 100%, but I never initiate a charge unless I have discharged the battery enough to accept full regeneration. I only recharge above 50% SOC if I need the range for a particular trip. I am usually down near LBW or VLBW before I charge. Almost all charging is off peak (at night) at home. I used QC once in December.

2. My round trip commute is 52 miles, mostly freeway with surface streets at each end and I always keep up with traffic in the HOV lane. I typically add a few miles of errands on surface streets. I also frequently use all 80 kW accelerating from stop lights.

3. The car is parked on concrete under covered parking either at my office or the airport. At home, it is either on the concrete driveway (in the shade of a tree during late afternoon) or in the garage.

4. Based on the bar graph (fuel gauge) and typical range, I am guessing that the car is at 60-65% SOC whenever it is parked for an extended period of time at the office or airport.

5. Over the past year, my battery temperature has ranged between 4 and 8 bars. Lately, it has been 6 after cooling overnight and 7 during the day. It spent a significant amount of time at 8 during the hottest part of last summer.

I may be the only Leaf owner in Phoenix who feels this way, but I am glad that Nissan chose not to use active battery cooling. As a field engineer, I like the "keep it simple" approach. Also, I would not want to return to the car to find a dead (or partially depleted) battery because the cooling system tried to keep it cool while I was gone.

I have been waiting for the LeafSCAN to become available, but am now thinking about ordering a Gid meter kit in the meantime to get something to monitor my battery.

Gerry

[phxsmiley]

I have a GID meter and would be willing to arrange to take a reading after a 100% charge, for those in the Chandler/Tempe/Phoenix area. Please send me a PM if you're interested and we can work out a time.

[DaveEV]

I have recorded charging energy from shutdown to 100% several times over the past year and have not seen a significant decrease.

This is really the best way to measure capacity - a discharge/range test and a charge test (measure full charge energy). It could be more reliable than the GID as the GID is likely compensated by some unknown factors.

A discharge test would be done over a known loop which is easy to repeat and preferably done down to at least VLBW if not turtle. Before the test, charge to 100% - I would suggest charging to 100% on L1 which should give the car more time to balance cells. Record miles traveled and dash reported economy at LBW, VLBW and turtle. I also recommend recording L1 time to 100% (Better (reverse) SOC meter already in the car?)

A charge test would drain the battery to LBW, VLBW or turtle and then record the amount of energy it takes to charge back up to 100%. Blinks can record this data - I would hesitate to recommend a Kill-A-Watt because it's been known to melt under L1 loads along with the time it would take to charge from turtle to 100%. It would be nice to have a meter that easily plugged in between a EVSE upgrade or other L2 - but this would likely cost at least $100 to build, so the Blink appears to be the best option here for those who have it.

[shrink]

I may be the only Leaf owner in Phoenix who feels this way, but I am glad that Nissan chose not to use active battery cooling. As a field engineer, I like the "keep it simple" approach. Also, I would not want to return to the car to find a dead (or partially depleted) battery because the cooling system tried to keep it cool while I was gone.

I have been waiting for the LeafSCAN to become available, but am now thinking about ordering a Gid meter kit in the meantime to get something to monitor my battery.
Gerry

Thanks for the input, Gerry. I still have all 12 capacity bars, too, but there's definitely some loss of range. LEAFfan's ScanGuage read 85.7% on my car about a month ago after a 100% charge. I'm sure he'd be willing to take a reading on your car as well if you're interested.

I couldn't disagree with you more about the battery cooling, or in Volt lingo, thermal management system (TMS). I'll link to a very interesting post about the Volt's TMS. A few highlights:

1)Your battery would never be fully depleted due to active cooling. It won't run if not plugged in with a SOC less than 75%.

2) Quoted from the linked post:

"there is a substantial lifetime difference between 21C (70F) and 32C (90F) in the lithium-manganese batteries (which have the highest heat sensitivity/degradation profile of all lithium battery chemistries) that GM is using in the Volt. At 60% SOC, lithium-manganese batteries have a little over 8 year life at 21C (70F) but only a 5 year life at 32C (90F). At higher states of charge, the heat sensitivity and degradation rate is even greater."

3) The insulation of the TMS alone will slow heat conduction to some degree.

Here's the full link:

http://gm-volt.com/forum/showthread.php ... #post45948" onclick="window.open(this.href);return false;

Anyway, glad to hear you haven't noticed any loss of capacity, but please do keep us posted.

[RegGuheert]

I feel a need to provide at least 1 data point showing that not all Phoenix Leafs are losing significant battery capacity: After 12 months and 11,400 miles, I still have 12 bars and, as far as I can tell, have not lost significant capacity. Since I do not have a Gid meter, my method to keep track of battery capacity has been to record charging energy. I have recorded charging energy from shutdown to 100% several times over the past year and have not seen a significant decrease. My capacity may have started out a bit lower than others have reported, but it has dropped very little over the past year. I need to get the data entered into a suitable spreadsheet to post.

Thanks for the encouraging report, Gerry! I think the data you have is quite unique since it sounds like it covers the entire 12 months since you received the car. I look forward to seeing more details!

[Herm]

At 60% SOC, lithium-manganese batteries have a little over 8 year life at 21C (70F) but only a 5 year life at 32C (90F). At higher states of charge, the heat sensitivity and degradation rate is even greater."

Since the average temperature in Phoenix is 82° F then that battery will last a bit more than 5 years. More if Nissan tweaked the electrolyte.

[vegastar]

But there are 3 months with average temperatures higher than 90ºF (July the hottest with 95ºF average temperature), and the pack probably experiences higher average temperatures than the ambient temperature because of the heat generated during charging and driving. As the degradation is non linearly accelerated with these higher temperatures, they probably experience (much) more degradation than a pack with an average temperature of 82ºF. It is the same principle that driving at a fixed speed of 90 km/h consumes less energy than driving half the trip at 120km/ and the rest at 60km/h (90 km/h average).

And I believe last summer the temperatures where way above the average...

[Stoaty]

I feel a need to provide at least 1 data point showing that not all Phoenix Leafs are losing significant battery capacity: After 12 months and 11,400 miles, I still have 12 bars and, as far as I can tell, have not lost significant capacity. Since I do not have a Gid meter, my method to keep track of battery capacity has been to record charging energy. I have recorded charging energy from shutdown to 100% several times over the past year and have not seen a significant decrease. My capacity may have started out a bit lower than others have reported, but it has dropped very little over the past year.

While this is interesting and somewhat encouraging, the best way we currently have to compare cars is to use the Gid-o-meter on a fully charged and well-balanced battery. Otherwise, there are too many variables that may affect the result. The Gid-o-meter has been a very good predictor of when someone is about to lose a capacity bar.

[DaveinOlyWA]

At 60% SOC, lithium-manganese batteries have a little over 8 year life at 21C (70F) but only a 5 year life at 32C (90F). At higher states of charge, the heat sensitivity and degradation rate is even greater."

Since the average temperature in Phoenix is 82° F then that battery will last a bit more than 5 years. More if Nissan tweaked the electrolyte.

but spends over 14 hours a day in summer at 100+ which probably will bring it back under 5 years. wondering what Nissan will do when the first pack hits 70%? by that time, packs from TN should be plentiful