Charging from 80% to 100% -- What's the issue?

[Pipcecil]

I honestly don't believe letting the vehicle sit @ 100% is determinetal to the battery. We have tons of Li-ion batteries around in so many devices. Hitting 100% and staying that way isn't optimal but degredation is minmal at best (how many of yall charge your li-ion power tool batteries almost to full to leave them sitting until the next weekend? Everyone just charges to full). Now, the longer the battery sits @ 100% the worse it is for the battery. That I can agree. But I am thinking of order of magnitude different than a few hours (if a few hours @ 100% destroyed the battery it would have been scrapped for a different chemistry - that is just not feasible, ever). Knowing a bit about battery chemistry would leave me to believe that is right.

Now leaving the car @ 100% for a week ALL the time and only driving it once a week...eh, i can see some noticable degredation happening after awhile. Leave it a long time @ 100% for a couple weeks or more (even if its just once) - that probably will hurt the battery some.

Li-ion chemistry is fairly forgiving. No memory loss, quick charge and discharge. Li-ion batteries degrade for three reasons:

1. Time. The second they leave the line they start to degrade evetually the battery will no longer hold a charge, its just inherit in the structure of the battery. There is no way to change this. The battery will have a max set life the second it leaves the factory.

2. Heat. Heat is killer for Li-ions. Thats why the DC chargers stop. If you DC charge as much as I have, the % charge varies quite a bit from 80% - 100%. Its the heat that shuts the system down (to prevent battery damage). In the winter, the DC charger would want to go all the way to 95%+, in the summer, the second that sucker hits 80% it shuts off. This is also why the manual stats "don't plug in unless you have used x %). Li-ion batteries have no quals with "topping off", in fact, under use, they LOVE it. Its the heat generated by the resistence at the top end that is hurtful. As the battery charges, once you hit the top end, its slower and generates more heat byproduct. Its just nissan making sure that the battery doesn't get any heat damage. If you do this once it awhile, I wouldn't worry about it. But, if you find yourself doing it every day...not good.

3. Storage capacity. Have you read treatment of Li-ion batteries you purchase wholesale? Everyone comes with a care of battery storage. ALL say the same thing. If storing for multiple months (some say a month or more - but its always months) keep the battery at 50-60% for optimal life. That % is the sweet spot for Li-ion. Notice the time length. Arguing that leaving the car @ 100% over night is bad and your battery will die in 5 years is ludicrious. It takes a long time for the battery to sit at a high capacity for damage to be done. Also, never leave the car fully discharged, that will brick your battery, plug in as soon as possible!

If you notice all these issues (#2 and #3) talk about abudnant of over exposure and such. The damage done is all exponential. So the difference from a few hours to a few days is minutely small. But get to a week or so its start climbing that curve. The damage still occurs even on the short time frames, but its so small its hardly noticable. If you are shooting for the longest lasting battery record in the guiness book, then by all means follow everything to the T - always 80%, never store at 100%, never top off, don't DC charge, etc. You could probably squeeze maybe a couple of more years out of it before you reach the Time guage, maybe good for 11, 12, hell 14 years! But, lets face it. Few of us are going to try and shoot for a 14 year Leaf. Hell many won't carry it beyond 3 years and get something else. I wouldn't worry about battery degredation unless you hit the extreme times (i.e. leaving it for multiple weeks) or are shooting the car lasting you over 10 years.

My advice: If you can do 80% comfortably, then do it, every bit helps! Don't freat if you can't. The car is still built for 100% capacity and should last you plenty of years, more than you probably will keep it. And don't leave it at full for more than week untouched (I would say 2 weeks). And don't leave your car at 0%! ever!

[Ingineer]

Phil, where do you read the SOC % value and the stored capacity ? Does the car provide that data in the Nav windows, or do you get that using your own device which you had designed and installed in your car ?

thanks
Jay

Yes, See this thread.

-Phil

[Nubo]

- the higher end of charging is inefficient, in the sense that more electricity is spent to charge the last 20%

I don't know about inefficient (although it may be, I really don't know). But it's definitely slower. For the last 10% or so the charger tapers off the current drawn so while you normally get around 1 bar every 90 minutes hours on L1, the last bar may take 3 hours or so (I don't charge enough at L1 to know whether those are accurate, but that's the basic idea). So if you have the time anyway, that's fine, but on average you'll get more charge per hour if you start and end lower than you would if you start higher and end closer to 100%.

Also the slower charge time reduces efficiency since the coolant pump is running the whole time

[mkjayakumar]

Why is it that when I charge to 100%, the GOM says, 105 miles range

When I charge to 80% it is only 78 miles ? I would have expected around 82.

[mkjayakumar]

My bad. On the ECO mode it is indeed 85 miles at 80% which corresponds to 110 in 100%

[garygid]

There are three different % values being used, and sometimes being confused:

1. The Car's "80%" or "100%" charge levels. These are charge limit points most likely derived from the highest cell-pair voltages, near 4.10 volts. Presumably charging to "100%" (only about 94% True SOC) will take less time after the Pack loses 25% of its Capacity.

2. True SOC (TSOC): reported by Ingineer's LEAFSCAN device. Apparently this is just over 94% when the car has "charged to 100%". Most of us do not YET have access to this figure. After the Pack loses 25%, will a "100%" charge still indicate about 94% TSOC? If so, it is essentially useless (without an additional Capacity value) for computing Range.

3. The LEAF's "GID" value: GIDs generally indicate a value closer to "Usable Energy", not "True SOC". At 80 Wh per GID, this might be "Applied" (for charging) Energy, but Stored Energy is less, and Recoverable (Useful) Energy is even less. Since a typical new (full capacity) battery can show 281 GIDs when charged to "100%", a percentage of 281 is shown on the GID-Meter (SOC-Meter) as a percent of new-full Charge (not TSOC). If a Pack has lost 25% of its Capacity, we are likely to see this value, after a "100%" charge, indicate something like 75%, a useful indicator for estimating Range.

[mkjayakumar]

How do you guys calculate the GID values after a charge ? Is that off the wall from an L2 EVSE unit, or have you installed something specific to get this ? Currently I am using only 120V L1, Nissan supplied unit.

[garygid]

The GID value in internal to the LEAF, and not visible without special electronics to read the value from the car's OBD connector.

No, a typical OBDII reader will not help.

The "Leaf CANbus" sub-forum has threads that describe the "SOC-Meter" project that will display the GID value, along with other values, like Battery Pack voltage, current, and power.

This SOC-Meter (GID-Meter) project can be entirely DIY, but is also available as a Kit, or fully Built and Tested.

Also, see more info at:
http://www.wwwsite.com/puzzles/socmeter/" onclick="window.open(this.href);return false;

[Ingineer]

Gary's meter reads the Battery ECU's "Current Battery Level" as expressed in watt-hours when multiplied by 80. Therefore a typical number (my most recent "full" charge) is 22240 which Gary's meter shows as 278 "Gids". This is a useful number, but it's limited to a rather low resolution of 80 watt-hours. There is also much higher resolution data available. Here are some other parameters from the Battery ECU after that "full" charge on my Leaf:

Code: Select all

SoC: 94.591%    (Current State of Charge)
Lvl: 22.240kWh  (Current Level, i.e. 278 Gids)
Ful: 67.568Ah   (Full Capacity)
Tmp: 72.3f   	(Battery Temp)
Vlt: 393.23v 	(Battery Voltage)
CLC: 1.030   	(Grad Cap Loss Coef)
CLM: 1.005   	(Grad Cap Loss Mtr)
CPL: 92.3kW  	(Charge Power Limit)
RPL: 41.6kW  	(Regen Power Limit)
DPL: 110kW   	(Discharge Power Limit)

Last time I checked, my car opened it's main contactor after turtle mode at around 2% SoC. That means about the bottom 2% and the top 5% are not normally usable.

Using these numbers, I can calculate that if I were able to charge to 100% instead of ~95%, and discharge to zero, I'd actually have 23.512kWh total capacity. (Pretty close to 24kWh) Nissan does not allow the full use of the battery in order to ensure a long life.

The Battery ECU reports the full capacity on my Leaf is 67.568 amp-hours which means that the average voltage would be about 348, which sounds right to me.

All of this data comes from my new LEAFSCAN instrument that simply plugs into the Leaf. It's currently in development and I'm working as best I can on getting it out to everyone that wants one.

The Diagnostic connector located under the driver side dashboard gives access to the Leaf's internal networks which connect to it's various computers and modules. This connector is called a DLC3 (Data-Link Connector type 3), which is the same physical connector used for the OBD II system on cars with engines. Since the Leaf does not have an engine, it is not required by law to be OBD II compliant, and therefore it is not. This is why only devices specifically developed for the Leaf will work. The only one available now is Gary's meter, soon to be followed by LEAFSCAN.

-Phil

[garygid]

Values may have higher precision (more digits),
but that does not mean that they are more accurate.

For example: a value of 94.013% (high precision) could
still be wrong by 5% in some circumstances (low accuracy) !!!

A GID value of 50 could easily be "wrong" by 5% or 10%, so showing it as 50.123 GIDs does not increase its accuracy.