Other cars have a battery health thread so I thought it was time to have one for these cars! 
To gather information on the battery health you'll need Canion with a suitable OBD adaptor. An alternative on the C-Zero/Ion is Diagbox using a Lexia 3, or on the i-Miev, the MUT-III tool. I don't expect many people to have a Lexia 3 or MUT-III however. (I do have a Lexia 3 as well as Canion)
There are two main things of interest when looking at the battery health - one is state of health or SoH, the other is cell balance after a moderately deep discharge that would flag up any weak cells. Another lesser factor is cell resistance but this can only be found with Diagbox/MUT-III and is not available from Canion.
Unfortunately neither Canion or Diagbox give a direct SoH figure - they only report usable Ah capacity calculated by the BMS. SoH can be derived from the Ah figure, but only if you know what Ah figure should correspond to a 100% SoH, and this is also not stated in either Canion or Diagbox!
In short, nobody really knows for sure what Ah represents 100% SoH on these cars.
The raw capacity of the cells is 50Ah however they are operated over a reduced voltage range in the car (3.63 volts to 4.1 volts) than that used to specify their capacity, (2.7v to 4.2v I believe) so there would never be 50Ah usable even with brand new cells and making use of turtle mode range.
Charging cells to 4.1 volts instead of 4.2 volts reduces usable capacity by approximately 10% and from this and piecing together other information such as a single Canion reading taken on a warranty replacement pack on a US i-Miev, the generally accepted figure seems to be about 46Ah = 100% SoH, so that's what I use.
I have been recording the Ah figure vs date and mileage since I first bought the car, about 18 months ago first relatively infrequently using Diagbox (since it's a pain to connect and set up) and then more frequently using Canion. I definitely have some anomalous changes in the Ah figure over time so I thought I'd share these for discussion and comparison with others.
I have them recorded and graphed in excel, see below:
![Image]()
![Image]()
I do also have a graph of SoH vs date but as I do almost exactly 1000 miles per month the graph looks identical, so I have no real way to tell how much degradation is related to miles driven and how much the passage of time. I also stopped recording cell resistance when I stopped using Diagbox, although I could check it again if I needed to.
As can be seen, everything looked fine up until around 40k miles, with a drop of approximately 0.1Ah per 1000 miles, when there was a precipitous drop from 38.9Ah to 37.6Ah.
Because my measurements up until 41k miles were very infrequent (only every several months) I don't know exactly when that drop occurred and whether it was one large drop or a series of smaller drops.
I was a bit concerned about this drop and wondered whether I should do the dealer "Battery calibration" procedure in Diagbox, to measure the true capacity. This is a process the basically runs the battery down to a specified voltage under controlled conditions, charges it back up and does a calibration based on that.
Doing this calibration resulted in the figure dropping from 37.6Ah to 36.1Ah. Whoops! This is the vertical downwards line on the graph...
Then after 10 days of normal driving it jumped back up to 37.1Ah all by itself. This just goes to show that while the real battery health never gets better over time, the BMS's estimate of battery health can sometimes rebound if a previous estimate was in error! Since then it has resumed a slow gradual decline.
The question is, did the battery suddenly get worse around 40k or had the BMS been over estimating the true capacity prior to that, and it had a calibration "wake up call" ?
I see roughly 0.1Ah decrease like clockwork every month/1000 miles or so (actually 838 miles when you calculate it) but it is highly likely that this decrease each month is predicted capacity loss based on the BMS's programmed in battery degradation model based on time and mileage.
Opportunities for the BMS to truly measure the capacity accurately don't come very often (as they need a relatively full discharge/charge cycle under favourable conditions, such as warm weather) so in between those opportunities it will follow an assumed degradation model programmed in by the manufacturer, occasionally corrected by actual measurements.
The second main factor of interest in looking at battery health is how well balanced the cell voltages are after a deep discharge of down to say 30% SoC. To do this you need to fully charge the car on a Level 2 charger until the charging stops. At this point the cell voltages should all be balanced within 5mV, which they are on mine.
Now use the car until the SoC reported in Canion is about 30% then look at the cell voltages. Here are mine at 30%:
![Image]()
As can be seen, Cells 25 and 70 are a little bit weaker than most others. Not enough yet to cause me concern, but a noticeable difference nevertheless that should be monitored to see if it worsens. (Which so far it hasn't)
Is this the cause of the sudden drop in estimated Ah capacity around 40k miles ? Unfortunately I was not checking the cell voltages prior to that so I have no way to know. For all I know it was already like that at 28k miles when I bought the car and is unrelated.
I would be interested to see other people's Ah figure for the mileage their car has done, and also see the cell voltage graph when discharged to about 30%. (Note: you must do a 100% Level 2 charge first to allow the cells to be top balanced or the result won't be valid as rapid charging does not balance the cells)
To gather information on the battery health you'll need Canion with a suitable OBD adaptor. An alternative on the C-Zero/Ion is Diagbox using a Lexia 3, or on the i-Miev, the MUT-III tool. I don't expect many people to have a Lexia 3 or MUT-III however. (I do have a Lexia 3 as well as Canion)
There are two main things of interest when looking at the battery health - one is state of health or SoH, the other is cell balance after a moderately deep discharge that would flag up any weak cells. Another lesser factor is cell resistance but this can only be found with Diagbox/MUT-III and is not available from Canion.
Unfortunately neither Canion or Diagbox give a direct SoH figure - they only report usable Ah capacity calculated by the BMS. SoH can be derived from the Ah figure, but only if you know what Ah figure should correspond to a 100% SoH, and this is also not stated in either Canion or Diagbox!
In short, nobody really knows for sure what Ah represents 100% SoH on these cars.
The raw capacity of the cells is 50Ah however they are operated over a reduced voltage range in the car (3.63 volts to 4.1 volts) than that used to specify their capacity, (2.7v to 4.2v I believe) so there would never be 50Ah usable even with brand new cells and making use of turtle mode range.
Charging cells to 4.1 volts instead of 4.2 volts reduces usable capacity by approximately 10% and from this and piecing together other information such as a single Canion reading taken on a warranty replacement pack on a US i-Miev, the generally accepted figure seems to be about 46Ah = 100% SoH, so that's what I use.
I have been recording the Ah figure vs date and mileage since I first bought the car, about 18 months ago first relatively infrequently using Diagbox (since it's a pain to connect and set up) and then more frequently using Canion. I definitely have some anomalous changes in the Ah figure over time so I thought I'd share these for discussion and comparison with others.
I have them recorded and graphed in excel, see below:
I do also have a graph of SoH vs date but as I do almost exactly 1000 miles per month the graph looks identical, so I have no real way to tell how much degradation is related to miles driven and how much the passage of time. I also stopped recording cell resistance when I stopped using Diagbox, although I could check it again if I needed to.
As can be seen, everything looked fine up until around 40k miles, with a drop of approximately 0.1Ah per 1000 miles, when there was a precipitous drop from 38.9Ah to 37.6Ah.
Because my measurements up until 41k miles were very infrequent (only every several months) I don't know exactly when that drop occurred and whether it was one large drop or a series of smaller drops.
I was a bit concerned about this drop and wondered whether I should do the dealer "Battery calibration" procedure in Diagbox, to measure the true capacity. This is a process the basically runs the battery down to a specified voltage under controlled conditions, charges it back up and does a calibration based on that.
Doing this calibration resulted in the figure dropping from 37.6Ah to 36.1Ah. Whoops!
This is the vertical downwards line on the graph...Then after 10 days of normal driving it jumped back up to 37.1Ah all by itself. This just goes to show that while the real battery health never gets better over time, the BMS's estimate of battery health can sometimes rebound if a previous estimate was in error! Since then it has resumed a slow gradual decline.
The question is, did the battery suddenly get worse around 40k or had the BMS been over estimating the true capacity prior to that, and it had a calibration "wake up call" ?
I see roughly 0.1Ah decrease like clockwork every month/1000 miles or so (actually 838 miles when you calculate it) but it is highly likely that this decrease each month is predicted capacity loss based on the BMS's programmed in battery degradation model based on time and mileage.
Opportunities for the BMS to truly measure the capacity accurately don't come very often (as they need a relatively full discharge/charge cycle under favourable conditions, such as warm weather) so in between those opportunities it will follow an assumed degradation model programmed in by the manufacturer, occasionally corrected by actual measurements.
The second main factor of interest in looking at battery health is how well balanced the cell voltages are after a deep discharge of down to say 30% SoC. To do this you need to fully charge the car on a Level 2 charger until the charging stops. At this point the cell voltages should all be balanced within 5mV, which they are on mine.
Now use the car until the SoC reported in Canion is about 30% then look at the cell voltages. Here are mine at 30%:
As can be seen, Cells 25 and 70 are a little bit weaker than most others. Not enough yet to cause me concern, but a noticeable difference nevertheless that should be monitored to see if it worsens. (Which so far it hasn't)
Is this the cause of the sudden drop in estimated Ah capacity around 40k miles ? Unfortunately I was not checking the cell voltages prior to that so I have no way to know. For all I know it was already like that at 28k miles when I bought the car and is unrelated.
I would be interested to see other people's Ah figure for the mileage their car has done, and also see the cell voltage graph when discharged to about 30%. (Note: you must do a 100% Level 2 charge first to allow the cells to be top balanced or the result won't be valid as rapid charging does not balance the cells)
