Battery Degradation

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Hi Tony,

Could you give us a count on how many times you've done an extended charge or some estimated total miles driven on extended charge?
 
Khaihon said:
Hi Tony,

Could you give us a count on how many times you've done an extended charge or some estimated total miles driven on extended charge?

20% ?

Heat is the number one killer, and leaving it at 100% charge for extended periods is bad, but the two together are absolutely brutal.

Don't let all those scary pop up messages stop you from charging to 100% if you need it. I only charge to 100% for a trip that I will actually need it.
 
If you charge to 100% each time but use the car fairly soon after, would that still cause degradation? For example, using car for commuting, so at work and at home each evening, charge to 100% then use for commute.

Is that what you mean by "extended range", only approx 20% of the time you charge to full?

A Leaf dealer recommended to only charge to 80% consistently unless you plan to go on long trip but I know Leaf has issues with their battery.

Thanks.
 
EVlearner said:
If you charge to 100% each time but use the car fairly soon after, would that still cause degradation? For example, using car for commuting, so at work and at home each evening, charge to 100% then use for commute.

Degradation can't be stopped. It can only be slowed down. I don't know what the perfect long life temperature is for these Panasonic 18650 cells, but presumably something quite cold. Since we don't live in that world, just do your best to keep the cells as cool as possible.

Yes, charge to 100% is fine, but drive the car! Don't let it sit for days/weeks/months at 100%. Leaving the battery at 50% is best for storage.

Cold an 50%. Everything else is a compromise. Hot and 100% is the worst.

Is that what you mean by "extended range", only approx 20% of the time you charge to full?

Yes, "extended range" in ToyotaTalk (TM) means a fully charged battery to 100%. I charge to 100% about 20% of my total charges.

A Leaf dealer recommended to only charge to 80% consistently unless you plan to go on long trip but I know Leaf has issues with their battery.

Yes, Nissan has brought that image of problem batteries on themselves. They built a battery that is sensitive to heat and sold it in the hottest place in the USA without any temperature controls.
 
Thanks for the info.
I don't know why I feel so differently about battery degradation.. in ICE, the transmission wears out after X miles, or the belts and hoses wear out, etc and they get replaced. I suppose after X% degradation, you would just get a new battery.

If I may ask, did you from the beginning always take very good care of your battery (that is, you only left car at 50% when parked for extended periods, car/battery not left in high heat, etc)? Your case would seem like a really best case scenario -- you take care of battery and still see this % of loss. And do you think the loss would be linear, so at 40,000 miles, one may expect 14% degradation?

Or I'm hoping you will say in the beginning you didn't quite take such care with battery and learned along the way, which means that for people new to EVs who do pay attention, they should experience less loss. And to follow the thought, now that you are taking better care of battery, the loss is not linear but maybe at 40,000 miles, only 10% degradation or something like that.

I know EV and battery technology so new, so maybe we won't know the answer until years from now, when cars are being returned, people reporting their experience.

I appreciate you sharing your experiences and knowledge!
 
That's actually not too bad. Even if the loss was linear, you'd still have a car with greater range after 100k miles than a new Leaf off the lot. But from what I've seen, capacity loss is not linear, rather it drops faster at the beginning of life and then flattens out. My testing of cells simulating 20k miles of use show ~4.5% loss. Of course my cells are in an air conditioned room and are cycling/charging constantly, so probably have a better environment than even Tony's. Surprisingly, repeatedly using Extended charge setting (actually 95% State of Charge to the cell) every time seems to have a negligible difference in capacity (~1%) than the cells that are being charged with Standard charge (80% SOC).
 
EVlearner said:
Thanks for the info.
I don't know why I feel so differently about battery degradation.. in ICE, the transmission wears out after X miles, or the belts and hoses wear out, etc and they get replaced. I suppose after X% degradation, you would just get a new battery.

Well, I think the battery will be around $36,000 from Toyota (through Tesla), so it's unlikely a factory new battery would be installed. You'd just get a new car.

But, there will be folks who will rebuild them, as we learn exactly what Tesla did to the pack. If they used 2200ma batteries, it might not be that expensive. My guessimate of 4500 cells at $2 to $3 dollars each, and you do all the labor to swap them, is only $9000 - $13,500. Add more money for 2900ma, 3100ma, 3500ma, or 4000ma and up.

If I may ask, did you from the beginning always take very good care of your battery (that is, you only left car at 50% when parked for extended periods, car/battery not left in high heat, etc)? Your case would seem like a really best case scenario -- you take care of battery and still see this % of loss. And do you think the loss would be linear, so at 40,000 miles, one may expect 14% degradation?

Yes, my car sat for about 3 weeks while I was in Italy, at 50% charge, with the wall charge station unplugged, and the 12 volt battery on a tender. I live in San Diego, so that should answer the "high heat" part (although it can get hot east of me). Loss won't be linear, and I expect that I am at the point where the degradation should slow slightly, so maybe 10%-12% at 40,000 miles (assuming all the same as the past in terms of usage, heat, cycling, etc).

60,000 miles should be around 13% - 15% ending up at 100,000 miles at about 20% loss. From there, at some point, it will begin a more accelerated path to "End Of Life" at 70% capacity.
 
You have to look at your driving behavior to see if the 100% charge will cause degradation or not.
Putting heat on the side (we already know that high heat at high SOC% will reduce both life, and capacity), it will depend on your discharge cycles.
On the Panasonic 18650's, you will get your first degradation at about 300 cycles. So, if you charge to 100%, and then drive it all the way down to empty every charge cycle, you should see a drop close to 300 charge/discharge cycles... But, if you charge to 100%, and only drop the battery pack by 40% every time, then it's about 2500 to 3000 cycles before you will see any degradation.
 
Thank you Tony, Kohler and Rayray for the information!
It seems less discouraging then what I originally thought.
 
Tesla powered Rav4 EV data:

In service November 2012. High utilization of over 2000 miles (3000km) per month. Never stored in a hot environment. The only time subject to over 100F / 38C degrees, the car was left on all day to run the battery temperature control (Rav4 EV only conditions the battery when on, while charging, or in the 15-20 minutes prior to scheduled departure of a timed preheat / precooling of the cabin).

Car is frequently cycled to low SOC%, as might be expected from high utilization. Never left parked for more than a few hours at high SOC%.

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

Full charge to turtle:

144.4 miles at 3.7 miles per kWh (270 watthours per mile) equals 39.0kWh

39.0 / 41.8kWh = 93.3% capacity

6.7% degradation at 20,000 miles, 9 months in service.

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

Yesterday, drove with full charge to about 6 miles remaining:

18 months in service, 36,000 miles

94 miles driven miles plus 6 miles remaining at 2.7 miles per kWh (370 watthours per mile) equals 37.0kWh

37.0 / 41.8kWh = 88.5% capacity

11.5% degradation at 36,000 miles, 18 months in service.

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

NOTE: these are single data point observations, and not exhaustive research.
 
In service date 3/4/2013, Inland Empire, 4 months a year highs over 90F, two weeks highs over 115F. Kept in garage that never exceeded 95F.

145.1 miles driven plus, 11 mile remaining at 3.8 m/kWh = 41.08 kWh.

41.08 / 41.8kWh = 98.3% capacity

1.7% degradation at 10,402 miles, 13 months in service.
 
On the Rav GOM where is 50% on the meter? Since in 80% charge when full all the bars are there....

is that above the half way mark?

or just below? Or just dead center? (then technically that's 40% right?)

I really need to get cracking this thing open... ughh.. holidays..
 
Hi Jason,

50% is 10/16 bars, so slightly above halfway.

Standard charge (80%) is 16/16 bars and extended charge is also 16/16 bars. Very silly and it would have been nice if they shown some other indication of it an extended 100% charge.


Here's a reference to Tony's posts about that.
http://www.myrav4ev.com/forum/viewtopic.php?p=251#p251
 
Just out of curiosity, has anybody measured the pack voltage while charging to see how it correlates to the bar graphs? I just read Tony's link on the gauge and bars,etc but that just seems strange. So really, 50% is 1 to 2 bars above halfway and where I should be leaving the car sit (technically 40-50% so anywhere in between 6 to 8 bars)..
 
Each bar on the RAV4 EV represents 5% SOC. 10 bars is 50%.

Inexplicably, the RAV4 EV engineers did not put bars representing a charge above 80% SOC on the dashboard, so when you do an extended charge to 100% SOC, you will not see any change in the number of bars for quite some time, not until you hit 75% SOC. There are a number of idiosyncratic design decisions with the RAV, but that one is, IMO, certainly the weirdest of the bunch.
 
10-4 on that. Because now of this, I won't be letting the vehicle sit at 4-6 bars like I have been for the last 3 months which is 40-50% on a Leaf (3.82-3.85v).. But a 18650 should be sitting nicely at 3.7v range for 50% storage for avg 2-3% loss per year.

What a wacky gauge... :roll:
 
TonyWilliams said:
Just did a full charge to turtle yesterday:

144.4 miles at 3.7 miles per kWh equals 39.0kWh

39.0 / 41.8kWh = 93.3% capacity

6.7% degradation at 20,000 miles, 9 months in service.

So i think a source of error here is that you only have 2 significant digits in the "miles per kWH" number.
If it says 3.7 miles/kwh that means somewhere between 3.65 and 3.74 miles/kwh.
(going beyond 3 significant digits is useless because we only know the battery capacity to 3 sig figures)

Doing the calculation at both extremes:

144.4 * 3.749 miles/kWH = 38.52 kWH = 92.1% = 7.85% degredation
144.4 * 3.650 miles/kWH = 39.56 kWH = 94.6% = 5.35% degredation

So 6.7% +/- 1.3% degradatin is probably the best way to state that.

I'm at about 13K miles and 1 year of service and i think i'm starting to notice a bit of degradation myself, but i dont really have the opportunity to do long constant-speed tests to check it out. I may get to do that when i drive to Los Angeles where i'll be keeping really careful records.

I assume you're getting your mi/kwh number from the little screen that displays every time you turn the car off and you're driving at fairly low speeds to get 3.7mi/kwh?
 
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