Carsten said:
I have a 2012 MiEV, bought in summer 2013, with about 88,000mi and get a summer range of about 40mi driving country roads and in a small town. The range dropped abruptly after about 40,000mi and I started to have a dead 12V battery, if I didn't use it for a couple of days. Over the years I have swapped a couple of these under warranty. Do these 2 things go together and are these related to the "potential low durability..." letter from Mitsubishi. I love this little and simple car, but the battery degradation(low charging?) is detrimental to its use. EvBatMon shows 25Ah and 52PMC. I will be with Mitsubishi on Monday.
Do failing 12v batteries and failing traction batteries (low range) go together ? My answer would almost certainly be no.
Correlation (both starting to give trouble at about the same age) does not equal causation. Lead acid batteries only last a certain number of years before they need replacing and a 2012 car is now at an age where the 12v battery is well past due. However there is nothing that a failing 12v battery can do to cause cells in the traction battery to fail, or affect the range.
I replaced the 12v battery in my 2011 Ion this year (8 years old) and it was absolutely stuffed. The Ah capacity should be about 34Ah and it was measured at only 1Ah when I tested it outside the car. Yet the car was still running. Because there is no starter motor and the load is provided by the DC-DC charger when the car is in READY or is charging, the 12v battery doesn't have much to do except "start" the car power powering the ECU's and high voltage contactors, and provide a ballast once running, so it can get very VERY bad before symptoms are noticed, unlike in an ICE where it will fail to turn over the starter and be replaced long before it got that bad.
However as for the range dropping abruptly after 40k miles I'm afraid you're not alone. I have this problem now too. I bought my 2011 car in 2017 with 28k miles on the clock - at the time the traction battery was at 39.9Ah (good for its age compared to other cars) and summer range was around 65 miles, winter range around 43 miles. It's now at 56k miles and battery Ah capacity is down to 32.6Ah, summer range is about 54 miles, winter range about 35 miles, a massive loss to the point that I can't make my commute in winter without a rapid charge on the way home.
I have been keeping a record of the degradation and it started to accelerate dramatically around 40k miles, and I'm not the only one to experience this - I'm aware of a couple of other cars that have behaved the same.
Before 40k miles the degradation rate was about 0.1Ah / 1000 miles. It is now at about 0.4Ah / 1000 miles so dropping very rapidly and at this rate the car will be unusable to me within a year. In my case I believe that 3 cells have gone "bad" around 40k miles. For a full deep dive into the problems with my battery pack check our my "Is my battery dying" thread. You can read it from the beginning if you like however you may be better to jump to this post near the end first which has the conclusions after 2 years monitoring:
http://myimiev.com/forum/viewtopic.php?f=23&t=4014&start=50#p39013
There is a very obvious knee in the degradation rate graph around 40k miles.
To see whether your car has the same issue, if you have an Android device, you need to get yourself the free Android app Canion, and an OBDLink LX bluetooth adaptor to connect it to the car.
Using that app you can check the Ah capacity of the traction battery which will give you an overall measurement of the health of the battery - my guess is yours is in the very low 30Ah's by now (worse than mine) or even high 20's. For reference a new battery is 45.8Ah. It's possible to see whether this is overall degradation of all cells in the pack or just a few bad ones.
To do this you would charge the car up to 100% and let it finish balancing, then drive the car until the battery SoC as reported by Canion is down to about 20%, then switch to the voltage graph page and see if there are any outlier cells as in the graphs posted in my thread above - individual cells that are at a much lower voltage than the majority of cells at a low SoC are weak cells with a lower Ah capacity than the rest. The overall usable capacity of the pack is always limited to that of the weakest cell so it only takes one bad cell to kill your range.
I am going to do a cell swap of the faulty cells in the next few weeks so I may have a happy outcome for my car - I'm not expecting it to go back up to 39.9Ah, but even if it goes up to around 37Ah and the degradation rate drops back to 0.1Ah / 1000 miles that will be a win over what I have now.
Keep an eye on my thread over the coming weeks where I will post the results.
