Degredation impact of driving into bottom bars????

[cdherman]

I assume this has been addressed, but search could not really find the answer I desired...

I charge only to 80% and have a 33 mile round trip commute. During the Fall, things were fine, but on at least 2 occassions, I've now gotten home with only one charge bar showing (1 of 12, as opposed to 1 of the top 10).

Those two events were one day with AM temps at 12 deg F, and evening temps only about 20 F. The other day, I had a traffic jam to avoid and put some extra miles on....

But the question I have is not really range or driving style (I often exceed 70 mph, so my crappy range has other explainations).

I have read that using Li batteries in the bottom of their capacity is also damaging. Is there someone who knows more about this in the specific case of the Leaf?

I *bought* as opposed to leased and I'd like to know how using the bottom two bars is going to impact my battery life.

Any knowledge, facts... Opinions???

Several generic Li technology battery sources indicate that their longevity is best if NEVER charged over 80% or discharged below 20-30%. Does the Leaf have enough "hidden" capacity in the turtle mode that I can safely take it down to one or even zero bars showing withough damaging the batter unduely?

 

[surfingslovak]

That's a fair question, which has indeed been discussed many times on the forum. The textbook answer is 20% to 80% SOC. In the LEAF, this roughly corresponds to cycling the battery between the first low battery warning (LBW) and 80% charge. Patrick Connor wrote a nice article on that last year: Eight Tips to Extend Battery Life of Your Electric Car.

However, given what we have seen in the field over the past two years, personally, I would worry about sustained high ambient temperatures, solar loading in the summer in southern locales, leaving the battery fully charged for days and weeks, and regular high-speed hill climbs. Perhaps that's just me, but only then I would worry about low state of charge, occasional quick charging, and some of the other factors. Although it's just an approximation, Stoaty's model indicates that cycling losses will be drowned out by calendar losses in the first few years of ownership.

While it's good to err on the side of caution, unless you were putting a ton of miles on the LEAF, cycling losses, and by extension charging habits, will not have an appreciable and significant impact on the battery. Perhaps this is one of the reasons for all the positive annual battery reports. Most owners get five stars without going out of their way or trying very hard.

 

[FairwoodRed]

I have read that using Li batteries in the bottom of their capacity is also damaging. Is there someone who knows more about this in the specific case of the Leaf?

Cdherman, that is a huge question. I know that I have asked for Nissan to officially tells us Battery Pack Care Best Practices, but so far they have been largely quiet – leaving us to guess based on similar chemistry like surfingslovak pointed out above.

I also bought (78-month loan) so I also have some concerns about what it will take to make the pack last long enough. Fortunately, I live in Seattle, one of the best climates for the Leaf, and that could be the biggest factor in determining pack life.

Having said that, my commute is 50+ miles round trip (105 on Wednesdays). I am currently at 35,000 miles in 19 months. I have hit low battery warning way to many times to count – very low battery many times, but I didn’t keep a count (50?). I also charge to 100% every morning. I am currently showing ~260 GIDs and I estimate the my capacity loss so far is only 7.5%.

Also, TaylorSFGuy is high mileage and having to get a full charge both at home and at work. Last I heard, he was at 60,000 miles and about 15% loss. That is the best facts that I can offer you, but they are all anecdotal.

I personally try to minimize the time my pack spends below 20% and above 80% by how I charge it. I still drive it as far as my needs are that day. If I’m low, then I add some charge and let the timer finish up overnight/before I leave for work.

Regarding “hidden capacity” there isn’t much. My memory says 2.5% at the top and 5% at the bottom, but my memory could be wrong – Wish I could find the great pack voltage graph for you tonight…

 

[planet4ever]

Several generic Li technology battery sources indicate that their longevity is best if NEVER charged over 80% or discharged below 20-30%. Does the Leaf have enough "hidden" capacity in the turtle mode that I can safely take it down to one or even zero bars showing withough damaging the batter unduely?

OK, let's get one thing straight here. The bottom two bars are not "red" and there is no problem with driving down to zero bars. Turtle doesn't start until well below zero bars. That 2.5% (or so) that FairwoodRed mentioned is not Turtle, but Stopped, the step after turtle. That is the point at which the car cuts power from the battery to protect it. You can still tow it or push it home and charge it. You haven't destroyed the battery, but you have probably reduced its life.

Here is the sequence:

1. Drop to two bars - the battery is still nearly a third full when you hit this :!:
2. Drop to one bar - the battery is about one quarter full.
3. Low Battery Warning - "miles remaining" starts flashing. You are a bit below 20%, as surfingslovak said.
   • Some time after that the last bar disappears, but we don't pay much attention to that.
4. Very Low Battery Warning - "miles remaining" shows 3 dashes instead of a number. You are now at about 10%.
5. Turtle lights up - consider this the end of the line, and find a safe place to stop. You may not even be able to go a quarter of a mile further.
6. Stopped. Automatic power down. The only thing left is your 12v battery.

Tony Williams maintains an excellent table which covers all this and much more. Go look at it, print it out, and keep it in your car.

I'm not a battery expert, nor even an engineer, but I've been living by what surfingslovak just told you, that 80% to LBW is the "nice to the battery" range (the 80-20 rule). I do go to "100%" (which is really 94%-95%) when I need it. I do go to VLBW or below it when I have to (a 95-5 rule). I've only gone to Turtle once, and that was just as an experiment driving around the block to see what it was like.

Ray

 

[TonyWilliams]

Update on 2013 SOC readout for a new battery. For a degraded battery, I can only assume that that there will be higher % for the battery warnings, since the 2013 LEAF readout is "usable" SOC based. At 50% degradation, a full charge would show 100%, therefore the fixed Gid value warnings would happen at roughly 30% and 10% "usable" SOC:

2013 LEAF SOC readout, New battery, no degradation:

15% - Low Battery Warning = Gid raw value 49 (17.4%) = Gid2 15.3%

5% - Very Low Battery = Gid raw value 24 (8.6%) = Gid2 6.2%

0% - Turtle = Gid raw value 7 (2.5%) = Gid2 0%

*************

2013 LEAF SOC readout, old battery, 50% degradation:

30% - Low Battery Warning = Gid raw value 49 (17.4%) = Gid2 15.3%

10% - Very Low Battery = Gid raw value 24 (8.6%) = Gid2 6.2%

0% - Turtle = Gid raw value 7 (2.5%) = Gid2 0%

*************

This compares to the following Gid2 formulas:

100 ((281 -7) / (281 - 7)) = 100% [fully charged new battery]

100 ((144 -7) / (281 - 7)) = 50% [half depleted new battery, or 50% degraded but fully charged]

100 ((49 - 7) / (281 - 7)) = 15.3% [Low Battery Warning]

100 ((24 - 7) / (281 - 7)) = 6.2% [Very Low Battery]

100 ((7 -7) / (281 - 7)) = 0% [Turtle]

 

[Stoaty]

If you want to be extra conservative, I would charge the battery up to 2 full bars or 3 bars when you get home, then charge to whatever you need right before leaving in the morning. That is what I do, but we don't know how much difference (if any) it makes. Of course, it is easy for me because I generally arrive home with around 30-35% Gids (which should mean a slightly higher SOC) so I don't have to do anything special. However, if I go lower on a weekend trip I wait an hour for the battery to cool down and add some charge to get the battery back to 30-40% Gids, which is probably the sweet spot for storage.

PS It would be nice if Nissan included a "storage" charge option that put the Leaf at the sweet spot SOC for more extended time away (a week or more). It's easy for me to do this manually since I have a Gid meter and 10 minutes of L2 charge adds about 3% Gids, but others might benefit from this addition.

 

[KJD]

I personally try to minimize the time my pack spends below 20% and above 80% by how I charge it. I still drive it as far as my needs are that day. If I’m low, then I add some charge and let the timer finish up overnight/before I leave for work.

This is very good advice and the one that I try and follow.

If I need lots of range that day then I charge to 100% and I use the charge timer to make if finish just before I leave for the day.