Replacing the single cells in the battery pack?

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Active member
Dec 2, 2023
Hi everyone,
ThI’m new here but I was reading your posts since September.
After some superficial research I’m thinking of buying few cells and putting them in the battery packs instead of bad ones.
Not interested in getting original second hand ones but buying some alternative ones with closest specifications to the originals.
For example:

Any thoughts and experiences?
Did your warranty expire?

I've seen other people switch cells in car batteries on YouTube (for other car brands).

I think the main problem is getting the correct cells, you need ones with the same specifications.

You'll have to research that a bit more than just superficially.
The cell you link to looks like the E400, but it doesn't have any marking or serial number on it.

The E375 cell is a 37.5Ah cell. This is the cell used in the Kia Soul EV from June 2014 to June 2017.
The E400 cell is a 40.0 Ah cell. This is the cell used in the Kia Soul EV from June 2017 onwards.

Battery replacements for the first generation Kia Soul EVs are being done with second generation cells. There is about a 10% increase in energy capacity. Replacement packs have the same number of cells, in the same layout. Same physical size.

Here's a picture of 2 E375 cells laid out in parallel as a cell pair.

There is more detail about the E400 cell here :- Comparing Battery Chemistries
I’m doing the research, collecting lote of information and maybe in spring I’m going to do something about my car.
Can’t find original cells with 37.5 capacity on internet, would like to buy them of course.
Any idea how to get them?
My trouble started when the Turtle mode comes even with the « full » battery if I want to go faster or climb the hill. And is getting slowly worse.
On this forum I figured that it must be number of bad cells.
What will happen if I put 2 parallel 40Ah cells next to 37.5Ah cells together in same pack?
I'm no expert, but I've always learned to always use the same type of batteries; just like IanL said.

Perhaps there's a scrap yard / junk yard which has gotten an old / damaged Kia Soul where the battery is still good / undamaged? But in my country they never really sold well so there aren't many spare parts available at the scrap yards just because they hardly ever get one.
I also agree with Ian that you should use all cells of the same type and that the BMS should match.
This is what happened when my car got a replacement battery. All new cells and a new BMS.
My replacement battery works really well and is better than the original in two important ways.
Better range and better longevity. ( Better than the original car I bought in 2015! )
The E400 cells are much better than the E375.

But in the replacement or re-manafactured thread on this forum there are so many weird contradictions and behaviours of the re-manafactured packs. I do not know the reality of what is in these re-manafactured packs, but it seems to be mix-and-match. ( Mixing cells and/or mixing the BMS, depending on whatever they have available.)
These packs do not show the improvements I got. But it seems mix-and-match does work.


I used to own a Hyundai Blueon EV with a severely degraded battery. It had a range of 20km as long as you didn't drive fast, go up a hill, or tried to accelerate. Fine for a 5km commute on a slow road in summer, but otherwise a complete wreck. One cell had gone bad which stressed out the module it was in. I sold the car to someone who tried replacing the cells. The Hyundai Blueon EV used SK Innovation E250 cells. The same as the cells in the Kia Ray EV. But the cells taken from a scrapped Ray EV would not work in the Blueon.


Good luck with your DIY battery project. Please post again with the results. It would be great if someone had success with this.

Finally got my OBD2 dongle and for now I’m using Car Scanner available on AppStore.
First reading for first 30 pairs shows me some consistency in all but pair No 1.
Pair 1 fluctuates from 2,5V (or less) to 4V
Other 29 pairs between 3.3V and 3.7V
This was with 25% battery left and driving through town 30-50km/h. Turtle mode would come if trying to accelerate to quick.
Tomorrow morning I’ll scan it from 100%, journey to work, just under 50km, usually left with 40/45%, no motorway, max 90km/h.
P.S. How to include some photos in my post? 😀
Here's some old data I posted a few years ago :- Battery Ageing Model
I also own a 2011 Hyundai BlueON. That car has a failed cell at #61. I use the voltage heatmap on the SoulEVSpy app to monitor that cell. While driving that cell goes as much as 0.36V LOWER than the rest. When charging starts that cell will instantly switch from being lower to being HIGHER than the rest. Charging will cease when that cell is 0.36V higher than the rest.

Note - when using data from the OBD we always refer to a cell pair as a single cell. This is because there is only 1 voltage sensor for each pair.
Some more info about failed packs can be found in this previous thread. :- Cells in HV battery
There's some interesting battery videos from Ukraine.
In the first one we see the swollen battery cell from a failed pack.
They show a video from a car that has an 80km GOM at 100% but turtles at 30km.
This is a very failed battery. Reminds me of my old Hyundai Blueon.

Finally an update on the remanufactured-packs
They are not just sending new cells to be replaced out in re manufactured packs.
It's a different part number and a very different price. One comes from the battery manufacturer in South Korea, the other comes from a re-manufacturing plant in Texas.
Looking at the Kia parts website - Kia Soul EV Re-manufactured Battery (37510-E4250R)
This battery costs $1,609.50 and fits all models both 27kWh and 30kWh
Looking at the Kia parts website - Kia Soul EV Replacement Battery (37510-E4250)
This battery costs $12,293.25 and fits all models both 27kWh and 30kWh

Opening those links today it now shows the remanufactured pack is no longer available. The replacement pack with discount costs $15,925.13
Thanks for reposting this old post, useful.
After today’s collected data I have already few ideas and lots of questions 🤣.
Cell no 1 (first pair) is definitely trouble maker.
All others are more or less similarly “old” and behave in same range.

While driving and monitoring this cell in with others, every time when it goes under 2.5V Turtle mode will come and limit power. If I slowed down enough that it goes back and stabilized around 3.2V Turtle mode will disappear and power will “come back “.

This is my issue. Turtle 🐢 mode. Could be full battery, if I accelerate to the point to deplete cell 1 I loose power and can’t drive decent speed, no more motorway for me for now 🤣.

But if I stop for few minutes, cell 1 gets charged by others, cell 2 before coz I see slight difference between 2 and 3,4,5….
That “gives back” some life to cell 1 even without plugging the car to charge and I can do some distance without trouble.

Autonomy is still satisfactory for me, 10% less than when I bought this car a year ago. I can make 90-100 km, more than enough to go to work but turtle 🐢 mode is the real problem.

Would like to attach few graphs 📈 from OBD but not sure how on this forum.
Ok, found out how to attach the photos…
This is what I have:
-cell (pair) 1 has 4.15V when I start with 100% charge
-cell 4 (almost all others have similar health) has 3.95V
-after the journey of 30km and with 65/70% left
no 1 has 3.4V and others 3.65V
-if accelerate to get no 1 under 2.5V Turtle 🐢 mode comes on.

My conclusions with help from experiences on this forum and reading the book “Battery University “:
-no 1 lost capacity, charges fast to 4.2V and discharges fast to the point of cut off by BMS
-due to the previous point, other cells cannot charge above 39.5V before BMS stops charge, and capacity of entire battery at 100% is reduced.
I have few ideas what I would like to try next, will soon post it…
I don't see that image either. I use firefox.
This forum will not allow users to upload images directly.
Instead you must link to an image uploaded elsewhere.
This is done using the 'Insert Image' icon in the bar above the text.
I recommend using one of the non-commercial image sites that has a lengthy history of operation.
If you ever look back at the 2015 posts so many of the images are missing because they were using commercial image sites that no longer exist.
To save bandwidth and to give my posts a consistent layout I always load a low-res image which hyperlinks to the high-res version.
This is done by wrapping the image tab with the 'Insert URL' icon.
Sorry for the image, I did copy it directly from iCloud. I can see it on my phone and iPad.
I’ll try to sign up onto Flicker…
Last post is the picture, same like the link above , but I can’t open it on my Apple gadgets.
Can you see it in the post? Please can somebody confirm.
If you can see my second photo…
Green graphic is average pair of cells,
Red graphic is bad cell no 1 which dictates car behavior,
Blue graphic is next bad cell no 96 which is much closer to average ones than to worst one.
Idea 1:
Somehow give the command to the BMS to isolate cell no 1 and not use it anymore. Like in Tesla system, isolate and forget about it. I guess that this will not be possible, nobody mentioned something like that being done before.
Idea 2:
Physically open battery pack, disconnect no 1 from the system. Then connect the second cell directly with new cable directly to beginning off the pack. Problem is that the sensor attached to the cell no 1 will show error and car will not run at all.
Idea 3:
Do same as above but connect the sensor from the bad cell to the closest normal cell (no 2 or 3). BMS will think that no 1 cell has same parameters like others. Could work.
Idea 4:
Bye pair off new cells and put in the place of no 1. Hard to find exactly the same, discontinued for model 2015. Closest available is 40Ah , 3.7V. Putting them as a pair, that will create capacity of 80Ah, instead of 75Ah. Not to forget that old ones are now even more feeble than original 75Ah. Discharging the new one below 70Ah before connecting could help because on the first charge the old ones will stop charging when one of them hits 4.2V. Should work.
Idea 5:
Buying pair of second hand original cells and hoping that they have similar capacity as mine.
Will work..?
These are my quick thoughts and ideas and will work on them to be sure how to proceed. I have some time coz I broke my wrist recently and can’t work on my car until later, hopefully in January.
Any thoughts, ideas, criticisms, experiences are more than welcome.