Help - how to interpret 1 year battery report

I have results of 1 year battery check of 5 iMiev, and not sure how to interpret them, your help needed:

1.
5870 km - distance traveled
90,5 % - state of charge
43,2 Ah - actual battery capacity
parked outside in temp often -30C (yes minus 30C)

2.
4677 km - distance traveled
68,0 % - state of charge
43,4 Ah - actual battery capacity
parked outside in temp often -30C

3.
5564 km - distance traveled
74,5 % - state of charge
41,8 Ah - actual battery capacity
parked outside in temp often -30C

4.
5891 km - distance traveled
87,5 % - state of charge
41,8 Ah - actual battery capacity
parked in garage

5.
11895 km - distance traveled
62 % - state of charge
42,7 Ah - actual battery capacity
parked outside in temp often -30C

Nominal battery capacity according to manufacturer is 50 Ah
Thank you for your help

If it really is a 16 Kw, 330 volt battery bank, the new capacity would be 48.5 AH

The reports you show with capacities in the low 40's remaining after 1 year would mean that the battery has lost about 15% of it's capacity, which also means that the cars have lost about 15% of their range. I *suspect* that these not so good numbers are probably due to the extremely cold temps . . . . cars stored at more 'normal' temps would (hopefully) do lots better

Mitsu *says* that the battery *should have* about 80% of it's capacity remaining after FIVE years, so either these batteries are not doing very well, or they lose most of that 20% the first year and then not much over the next 4 years

Don

Thank you. Is the 16 kWh user accessible, and if not is adjustment for usable capacity required. All comes down what base was used, but what owner was told that cars according to specification. car 4 was parked in garage but have lowest Ah value which may suggest that cold was not only factor.
Richard (owned 5 or maybe more Mitsu cars)

mitsu5, I suspect that you may have a slightly older battery technology than the present US-delivered vehicles. In any case, I wouldn't worry about it as your numbers are fairly close and your battery packs are still quite usable. It's nice to see that your highest-mileage vehicle has a capacity that is right in the middle of the group. Also interesting that the car that was garaged instead of being left outside actually was at the lower end of the AHr capacity. By California standards, your winters are awful

BTW, as Don pointed out, the only number of interest is the Ampere-Hour, as the State of Charge I presume is whatever charge level that particular battery happened to have at the time the test was started ... but, then, I would expect them to fully charge the car before performing a full capacity test, so why bother including the SOC number in the results to you? Maybe they took a shortcut and simply extrapolated the AHr starting with the SOC and then doing a quick load test. Anyone?

Mitsu5 - how long did their testing of each car take?

I do not know how long they did the tests because those are fleet cars.
I am not sure if US battery are different then European version but who knows (LEV50-4 here). Calculating according to what Don said losses for 1 year are 10.9, 10.5, 13.8, 13.8, and 12.0%. Assuming 80% after 5 years of ownership for the remaining 4 years losses should be just 3%/year and I am not sure if that possible. None of the car was used during extreme cold and if fact that temperature was only for few nights. I am not sure what will cause more damage to the battery cold or hot (+30C temp in the summer was for much longer than few really cold nights). According to the paper http://www.gs-yuasa.com/us/technic/vol5/pdf/05_1_021.pdf effect of high temp on battery temp can be substantial. We will see in the future

I had my 8 month service/battery calibration and here is the report:

http://i.imgur.com/nW5bQUp.jpg

I'm trying to figure out how much capacity I've lost. From what I gather, the key figure is "Battery Current Capacity: 46.1 Ah". Don has indicated in this thread that a new batter would have a capacity of 48.5 Ah, which would seem to indicate that I have lost about 5% of capacity. However, I've seen a number of websites that list the MiEV batter capacity as 50 Ah, which would mean I've lost almost 8% after only 8 months/ 8800 miles. That would really be troubling. I suppose a "state of charge" at 99% mitigates that a bit, but still these are worrisome numbers. Any thoughts?

PS. The fee for the 8 month service was $109 and I was told that the air filter looked good and wouldn't need replacing until 15,000 miles.

PPS. My MiEV had its 1 year birthday yesterday. Deducting the miles it had when I bought it, I put 8,400 miles on it in one year.

tonymil, if we do the math -

Our BMS allows the cells to charge to "only" 3.955v
Your measured capacity is supposedly 46.1Ah (how did they do that?)
We have 88 cells
Multiplying the three gets us to 16.045kWh
Sounds more than good enough to me.
Thank you for publishing the numbers.

tonymil said:

I'm trying to figure out how much capacity I've lost. From what I gather, the key figure is "Battery Current Capacity: 46.1 Ah". Don has indicated in this thread that a new batter would have a capacity of 48.5 Ah, which would seem to indicate that I have lost about 5% of capacity. However, I've seen a number of websites that list the MiEV batter capacity as 50 Ah, which would mean I've lost almost 8% after only 8 months/ 8800 miles. That would really be troubling. I suppose a "state of charge" at 99% mitigates that a bit, but still these are worrisome numbers. Any thoughts?

Click to expand...

Tony,

I don't think you can draw any meaningful comparison, since you don't have a report showing what the actual capacity was when you bought the car - Anything we compute is only a theoretical number and those tend to be a bit optimistic, in my opinion

I'm with Joe - It sounds very good to me and I wouldn't worry about it for a second. Now that you have some actual numbers for your particular car, you'll know better a year from now when you have it checked again because you'll have something to compare those new numbers to

Don

JoeS, Don, thanks for the feedback. I must have misunderstood the responses to mitsu5 and his readings. I have to say that I'm getting better RR readings on a full charge than I was before the re-calibration so I'm very happy about that. It's been a great year and I couldn't be happier with my MiEV, especially after driving the Mitsu dealer's loaner car for 2 days while they calibrated the MiEV. It was an older model Lancer wagon. What a POS. It smelled, it vibrated, it was noisy, the seats were uncomfortable, ugh. I was so happy to get my MiEV back!

Tony

tonymil, the only 'calibration' procedure that I am aware of is simply allowing the car to charge fully from two bars to 16 bars (until it stops charging). I don't know what else the shop does other than readout the capacity in ampere-hours (sure wish they would identify the current level that this reading is taken at). Interesting that the battery test printout given to iDriver identified the cell voltage and not the Ah capacity:
http://myimiev.com/forum/viewtopic.php?p=7365#p7365
Incidentally, all of us should be seeing better RR numbers, now that summer is coming...

JoeS said:

Incidentally, all of us should be seeing better RR numbers, now that summer is coming...

Click to expand...

I suppose if you're among the lucky ones who don't use the A/C during the summer months - We kinda look forward to Fall, Winter and Spring when we can get by with minimal climate control usage . . . . during the summer, we use the A/C every day, wherever we go

Don

JoeS said:

tonymil, if we do the math -

Our BMS allows the cells to charge to "only" 3.955v
Your measured capacity is supposedly 46.1Ah (how did they do that?)
We have 88 cells
Multiplying the three gets us to 16.045kWh
Sounds more than good enough to me.
Thank you for publishing the numbers.

Click to expand...

Actually wrong math.
The LEV50's are taken to about 3.955V at end of charge but the capacity of a battery pack is calculated at the nominal voltage at a given discharge rate. In the case of EV lithiums this is usually the 1hr rate (~50A).
The LEV50 nominal voltage is 3.7V so the correct calculation is 46.1 Ah x 3.7V x 88 cells = 15.01kWh.
If you look at a discharge curve for lithium you will see that the cell spends most of the discharge time at 3.7V as the top end voltage drops away within a few % discharge and then droops lower towards the end of the discharge.

The LEV50's start with 50Ah x 3.7V x 88 cells = 16.28kWh. (nominally though the vehicle BMS probably keeps a bit up its sleeve ?)

The temperature at which the battery capacity test is done is critical to the usefulness of the test.
The higher the temperature the higher the indicated capacity. Any battery test must state the actual cell temperature. The value is available on the CAN bus.

I look at getting battery capacity estimate a different way.
By logging the kWh on an external power meter for every recharge from new I can see that the iMiEV power meter is very accurate. (well at least within 1kWh).
Whatever the power meter reading is from full in kWh is what I put in from mains + 5% for charger efficiency (~95%.).
So if 1kWh remaining, the external power meter reads 15.0 to 16.5kWh once charge is completed.
The 1kWh is probably between 0.5 and 1.5kWh of course.

The fact is that after 12 months and 26,000km these numbers still check out and even though I have never gone below 1kWh indicated on power meter, I have still been putting in between 15 and 16.5kWh when 1kWh remaining on meter suggesting both a status quo in capacity and a likely capacity around 16kWh.
What I expect is that I will need to lose more than 1/16 of the battery capacity before it will show up on my spreadsheet.

A battery capacity test based on internal resistance and probably a readout of BMU estimates as done in the tests listed in earlier posts may be conservative ? Just try some real measurements with a power meter yourself.

Ozimiev said:

...The LEV50's are taken to about 3.955V at end of charge but the capacity of a battery pack is calculated at the nominal voltage at a given discharge rate. In the case of EV lithiums this is usually the 1hr rate (~50A).
The LEV50 nominal voltage is 3.7V so the correct calculation is 46.1 Ah x 3.7V x 88 cells = 15.01kWh.
If you look at a discharge curve for lithium you will see that the cell spends most of the discharge time at 3.7V as the top end voltage drops away within a few % discharge and then droops lower towards the end of the discharge.

Click to expand...

ozimiev, thank you for the correction and the further detailed explanation. Yes, capacity should be stated at the 'nominal' voltage, and temperature is presumably at room ambient (somewhere around 20degC).

Bottom line, we really do have very little to worry about with our traction battery packs, especially with tonymil's recent positive experience with Mitsubishi support.

Remember the numbers from the Mitsu5 five i-MiEV's 12 month report

1. 5870 km - distance traveled / 43,2 Ah - actual battery capacity
2. 4667 km - distance traveled / 43,4 Ah - actual battery capacity
3. 5564 km - distance traveled / 41,8 Ah - actual battery capacity
4. 5891 km - distance traveled / 41,8 Ah - actual battery capacity
5. 11895 km - distance traveled / 42,7 Ah - actual battery capacity

And tonymil 8 month report - 8800 miles (14.000 km)
State of charge (control value) - 99%
Battery current capacity - 46,1 Ah

Now my turn, 36 month report - 38750 miles (62.000 km)

State of charge (control value) - 96,5%
Battery current capacity - 36,4 Ah

I would like to see more of us presenting this values. I don´t understand the state of charge value, why the car don't charge 100%? Other thing, it can take 15,8 kWh from empty to full. I don't see how this is compatible with 36,4 Ah.

Malm, I wouldn't read too much into "capacity". I have yet to understand exactly how Mitsubishi and their MUT-3 performs this measurement/calculation. Without 100% cycling (i.e., full discharge to full charge at a very specific current), I don't quite understand how a quick-and-dirty test can produce accurate results - perhaps they select a couple of mid-range voltage points and count the Ah going in between those two points? About all we can say is that if MUT-3 does the test consistently, then we should have reasonable relative results.

Incidentally, over on the Australian forum there's a pertinent discussion relating to charger efficiency and what happens at the upper end (this post, and a few subsequent ones): http://forums.aeva.asn.au/imiev-measured-data_topic3870_post49845.html#49845

JoeS said:

Malm, I wouldn't read too much into "capacity". I have yet to understand exactly how Mitsubishi and their MUT-3 performs this measurement/calculation. Without 100% cycling (i.e., full discharge to full charge at a very specific current), I don't quite understand how a quick-and-dirty test can produce accurate results - perhaps they select a couple of mid-range voltage points and count the Ah going in between those two points? About all we can say is that if MUT-3 does the test consistently, then we should have reasonable relative results.

Incidentally, over on the Australian forum there's a pertinent discussion relating to charger efficiency and what happens at the upper end (this post, and a few subsequent ones): http://forums.aeva.asn.au/imiev-measured-data_topic3870_post49845.html#49845

Click to expand...

But i think its a good value to compare with the other cars. If it is taken allways in the same way, i can see if mine is more degradated then yours. Yes, in the end, if we stop charging at 97%, tha car will assume that have 100% and will not permit to charge more. I show in one of my videos the car going to 100% in the moment that I tryed to charge a little more over 95%.

Mitus5 wrote, in part, at the start of this thread...
"I have results of 1 year battery check of 5 iMiev, and not sure how to interpret them...."

Interesting and useful thread.
But what I want to know, since I'm coming up on one year of ownership, is this:

Mitsu5, how come you had this test done? (Maybe that was mentioned in this thread but if so I missed that.)

Am I required to stay under warrenty to take my MiEV in for any sort of service check, including that 1 year battery check? There is a timer on the odometer tha appears to be counting down to a one year checkup.
If so will I be charged for it?

There's that month countdown in the odometer and another that IIRR appears to be counting down to a 12,000 mile service checkup. Think they were both under the wrench icon.
Is there any way to turn those off? Not a critical issue, but curious.

Seems like based on this thread, except for the unlikely event of finding a serious battery issue, the value of the battery test is marginal at best. Not so?

Have any of you others gone in for a "one year service" and if so what were you charged for it in the USA?

I suppose I could call the local dealer and see what they say in regard to the above question, but thought I'd get feedback from here before I did that.

Thanks for any help.

Alex

Acensor, the service reminders can be easily cleared by a long press of the button, though taking the i-MiEV in for service should be done, but I don't think it's required. I took mine in, didn't cost anything, though my dealer didn't do much of a battery check. They did top off my wiper washer fluid for free.

As for a battery test, now that we have Canion, we can do our own battery check by watching cell voltages, temperatures, and the total energy out/in while driving or charging.

acensor said:

Am I required to stay under warrenty to take my MiEV in for any sort of service check, including that 1 year battery check?...Seems like based on this thread, except for the unlikely event of finding a serious battery issue, the value of the battery test is marginal at best. Not so?...Have any of you others gone in for a "one year service" and if so what were you charged for it in the USA? I suppose I could call the local dealer and see what they say in regard to the above question, but thought I'd get feedback from here before I did that.

Click to expand...

Alex, didn't we already address your questions on your very own thread Annual inspection and "required" maintainence? that was specific to that topic? - Maybe better than diluting this thread? :roll:

We haven't heard from Mitsu5 in over a year, and the data he was referring to was not his car but a fleet of Russian(?) i-MiEVs.

Mitsubish's February 2012 letter has made it clear that the battery pack does not need an annual "Capacity" test. As for all the other items, you can judge for yourself if you want to have someone do it for you. For myself, while I'm still able to, I prefer to crawl over and under my car and do my own inspections, thank you - my time to do this is far shorter than driving 30 miles to the Mitsu dealer and waiting for them to do their thing, and then paying them for the pleasure. Oh, and it takes less than a minute to replace the cabin air filter.

I am not aware of any warranty issues resulting from not having Mitsubishi perform these routine maintenance inspections instead of either doing them ourselves or having a local trusted mechanic do them for us.

"...Alex, didn't we already address your questions on your very own thread Annual inspection and "required" maintainence? that was specific to that topic? - Maybe better than diluting this thread? :roll: ..."


Yes, aged brain vaguely remembered that. Let's NOT pursue this in this thread. I'll put my question about resetting the odometer nagger over in that other thread.

Alex