Battery degradation

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jsantala

Well-known member
Joined
Sep 12, 2014
Messages
296
Location
Finland
I'm planning to purchase a 2011 Citroën C-Zero, the Citroën's variant of i-MiEV. It's been their floor model which they haven't been able to sell in three years, possibly due to the 35.000€ price tag. Don't worry, I'll get it for less than half of that. I don't know the miles on it yet, but I'm guessing they're very low and the car probably has been inside in warm storage for the most part.

So the question is, what kind of battery degradation have you observed in your own iMiEVs over the years and miles driven? I'm only interested in actual user reports, not hearsay or guesswork. How far can you go with your pack now compared to new?
 
I have an i-MiEV since april 2011. I'm from Portugal. The worst enemy of electric cars is the high temperatures, and the Nissan Leaf from Arizona showed that fast. My country is not so hot, but have high temperatures (more then 30º C) often in summer.

Most users with 2011 and 2012 will not see any difference. They will do now the same mileage (or very little difference) that they did two or three years ago. But that doesn't mean 0 degradation. That degradation maybe only can be found at very low SoC, and most of us avoid to take the car bellow 20% SoC.

In mine, there is clearly a difference between 2011 and 2014. Not easy to get the correct number, but I fill I lost between 10 to 15% of original capacity.

In Finland, because the high temperatures are not a problem, lost of capacity will not exceed 1 to 2%, I think.

If you want to know more of what an i-MiEV can do, you can watch some of my videos:

https://www.youtube.com/channel/UCtO0sVVtEd9B3a37X3XsNbw
 
Thanks for your reply, Maim. It's good to hear that the battery degradation in the i-MiEV and it's variants doesn't seem to be as bad as on the Leafs. I figured as much, since I haven't heard anyone complaining about it.

Heat is an issue, but as you said, it's not an issue around these parts. Last summer we got temperatures of over 30 degrees Celsius, but it's certainly not the norm here. Then again, who knows, the climate change seems to increase extreme weather phenomenon.

The real problem here is the cold. Lithium batteries don't particularly like to charge while frozen either. Remains to be seem what kind of a problem that ends up being, but I will try to figure out a way to heat my batteries, if at all possible. More on that on the Battery air intake post.
 
I *think* our battery degradation is hidden 'below the turtle' - In other words, in a brand new car when you see the turtle, you can drive another 15 Km or so before the car slows to a crawl. In a car with 30,000 Km's on it, that number might be reduced to 6 or 8 Km's and after another 30,000 Km's it may be reduced to none at all - The turtle shows and the car quits shortly afterward

So, what the user sees for the first few years is . . . . no degradation at all - The car still goes as far as it ever did before the turtle shows up and the RR numbers after a full recharge remain about the same, but . . . . the battery *is* ageing and it actually *is* losing a percentage of it's capacity - We just don't see it

That's my theory anyway

Don
 
jsantala said:
Don, is that just theory or actual first hand experience?
jsantala, I happen to agree with Don's theory, but the problem is that few of us are willing to take our cars down to turtle to test this theory. The closest to doing this is Malm, and you might peruse his posts to try to figure out what he's saying about this. In practice, I have over 32,000 miles (51.500km) on my USA (16kWh) i-MiEV and have yet to see any noticeable battery degradation (except for a stepped range decrease when I switched to non-OEM tires). As far as I'm concerned, battery degradation is a non-issue in the i-MiEV, but I do treat it properly in the hopes that it will serve us for well over 100,000 miles.
 
I'm just over 15,000 miles and pushed my car down to 8% yesterday (personal record low and well into turtle range), and my cells were holding 3.5 volts under a 25 kW load (half power). Even on the low end, my cells are pretty well balanced, with about a .1 volt stray at the worst. The car has the turtle reserve, and then the cells aren't even empty after the car reaches 0%. The portion between car 0% and battery 0% is where the hidden degradation is, which explains why Malm's car recalculated its capacity after 3 years of driving. His battery degraded to the point where it would hit low-voltage cutout while within the usable state of charge range. It recalculated to put low-voltage cutout back outside of the usable range. Now his car shuts down before the cells hit LVC.

My theory, of course.
 
If the cells in the iMiEVs are anything like the LiFePO4 cells (which they are not), then the capacity below the "knee" of the voltage drop is minimal. Once that voltage start dropping faster there's hardly any juice left. Again, at least on the LiFePO4 I've used to with my DIY projects. I've build a motorcycle with 40Ah cells and my car now has 60Ah cells. They just don't have quick charge which I'd need for longer trips. Unless I pack my car full of 400Ah cells, of course. ;)
 
As far as I can tell it seems to be pretty plastic-ee under there.

Here in the wintertime the temps also get pretty low in the -20s and -30s. I read on one post that leaving the pack charging using the level 1 charger at 8amps would be a good idea to keep the battery when the car is parked outside.
 
We've not noticed battery degradation in almost 20,000 miles. But, just two other comments on your potential purchase:

I'd have no hesitation buying the car in cold climates if I could at least park it in a garage overnight. It makes a lot of difference to have at least 10 to 20 C degree buffer over the outside cold (we got down to -15C a few times this past winter). The few times we had the car parked outside for an extended period cold soaking, it was hard to get the cabin to a bearable temperature (not warm, just bearable) and we took a pretty good range hit in those instances. Hopefully this winter won't be as bad (I guess Finland has winters like this all the time, but maybe that's just a common misconception.)

Regarding the % SOC theories and lithium, I can tell you I did experience that "cliff" once in my EV conversion. It was stupidly dramatic. Going kind of fine one moment, then - bamn, got to pull over and embarrassingly plead for charge the next. I think Mitsubishi must account for that "knee" much better than I can with my basic BMS/SOC information.
 
Yes, it can stay below -20C for days on end. I don't have a garage at my disposal at the moment, but getting the cabin heated is not a huge issue. We're quite used to using electric cabin heaters here and I'm also considering installing a gasoline heater and a small tank somewhere, possibly by relocating the 12V battery. It's still a lot better to burn half a liter of gasoline per hour when absolutely needed than driving a gasoline car and using several liters per hour around the year. I may also pre-heat the "coolant" with electricity as well.

So it's only the battery I'm worried about and actually I started another post on the subject, "Battery air intake", on the idea of pushing warm air into the pack at low temperatures. Especially since I'm planning to use the car around the year and make a 240km trip every week by quick charging 3-4 times along the way. I understand that the cold weather package on the Mitsu has some pack heating by air already, but I don't know if Citroën C-Zeroes have that.

Of course I'll soon find out some of the information anyway, but I just can't help myself and plan these things in advance. ;)
 
mixmike6 said:
As far as I can tell it seems to be pretty plastic-ee under there.

Here in the wintertime the temps also get pretty low in the -20s and -30s. I read on one post that leaving the pack charging using the level 1 charger at 8amps would be a good idea to keep the battery when the car is parked outside.

Yes, charging your car will warm the batteries and keep them at an optimum ambient temperature. I've followed this practice for the last two winters and get minimal range loss due to cold weather. If you have the CanIon app you can keep an eye on your battery temps and observe how your range reacts to lower temperatures. I only start charging before I need to use the car in the morning to make sure my batteries are at the warmest I can get instead of charging at night when I get home and letting the temperature drop. The drive home will keep the batteries warm until the next charge event.
 
MLucas said:
Yes, charging your car will warm the batteries and keep them at an optimum ambient temperature.

So we know that L1 charging burns up a higher percentage of incoming electricity in the balancing resistors than L2, and therefore takes EVen longer to reach full charge than a simple calculation would indicate (16 kWh / 960 Watts = 16.6 hrs ?).

So, is there any indication that L1 charging during winter is better for the battery because it keeps the cells warming longer? If you don't require max range, having the car plugged into L1 at all times it's not in use would keep the pack warm, but rarely at 100% SOC, which is also bad for longEVity. (Though remote preheat sucks on L1.)

When I get home from work and plug in for the night on L2, the car spends about 8 hours sitting at 100% SOC before it hits the road again... On L1, it spends nearly no time at 100% SOC.
Oh, to know whether a charging delay timer is worth the hassle... :roll:
 
Lithium cells are charged using a CC/CV pattern, in which the current is first kept at the maximum level (Contact Current) and then when a set level of voltage has been reached it is kept by lowering the current until the current goes to zero or close enough (Constant Voltage).

This is the main reason why a full charge takes longer than pack capacity divided by charging capability. You can observe this using a watt or current meter. You'll notice the current going down after around 80% charge. This slower, last phase can take a significant amount of time.

The fact that quick charge is usually 80% as well is not a coincidence. You can get to 80% pretty fast - which is when you reach max pack voltage - and it doesn't really matter how hard you push the electrons in until that point. After that it gets a little crowded in there and the electrons need to fit in before more can be accepted.

It's like a bar. When it's empty there's no queue and everyone gets in fast. When it starts to fill up a queue will form and everyone inside has to move a little for the newcomers to fit in. That is if you pack the bar really tight. It's not a good idea in a bar and similarly Lithium batteries also prefer if you don't stuff them too full.
 
DaveMiller said:
jsantala said:
.... the current is first kept at the maximum level (Contact Current) .....
Isn't CC constant current, not contact current?
Dave

Correct Dave, but I think that jsantala is doing very well posting in a foreign language! As my imported wife constantly reminds me, English is one screwed-up means of communication, but the most logical outcome, since it's a bastardized amalgamation of so many other tongues... ;)
 
jsantala said:
...It's like a bar. When it's empty there's no queue and everyone gets in fast. When it starts to fill up a queue will form and everyone inside has to move a little for the newcomers to fit in. That is if you pack the bar really tight. It's not a good idea in a bar and similarly Lithium batteries also prefer if you don't stuff them too full.
jsantala, that is a wonderful analogy! :lol: :geek: :lol: BTW, don't worry, your command of what passes as English nowadays is excellent, and I think we all knew what you meant!
 
jray3 said:
So, is there any indication that L1 charging during winter is better for the battery because it keeps the cells warming longer? If you don't require max range, having the car plugged into L1 at all times it's not in use would keep the pack warm, but rarely at 100% SOC, which is also bad for longEVity. (Though remote preheat sucks on L1.)

When I get home from work and plug in for the night on L2, the car spends about 8 hours sitting at 100% SOC before it hits the road again... On L1, it spends nearly no time at 100% SOC.
Oh, to know whether a charging delay timer is worth the hassle... :roll:
If the car is kept outside in below freezing temps, I would think L1 would be best for exactly the reason you stated - The pack could be kept on charge all night long (and therefore warmed up) and hopefully be just about full when you need it in the morning

You would have to switch to L2 to get any sort of meaningful preheat in the morning though before you took off

Don
 
Yes, it was just a typo. With the kids running around you just end up typing fast and not going back to check each word. ;)

I'm hoping Citroën has been smart enough to enable heating during charging, which I guess is sort of L2 to you, the slowest option available to us Europeans is 16 amps at 230 volts. I may have to get a J1772 cable with a button to select a lower amperage in case I need to charge from a 10A outlet. Our households generally have 10A fuses in most places with 16A for the kitchen, bathroom and usually outside outlets as well. All 230 volts obviously.

Parking lots in apartment houses usually have a outlet pole shared by two spaces, with one outlet for one car. In most cases they have a built-in 2 hour timer. It also has a shared 16A fuse for two cars, so I'll have to make sure I won't charge while the neighbours car is being warmed.

I'll be taking the C-Zero for a test drive in a couple of hours and hopefully I'll be taking it home later.
 
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