I Replaced All the Cells in my Leaf's Battery- Now I Have Some Problems

So I guess in a way the change was immediate but there were too many variables to really tell. That replacement cell for the one I punctured? It was super out of whack with all the other cells. Using leaf spy, it hit as much as 120mv of difference between the others. This could have limited the charging of the other cells, preventing us from getting more range. Perhaps it just took 9 months for the battery to balance.

It has been a while since I've looked at leaf spy but I can check it out and see if the battery has balanced. I don't have the car right now but I'll check on it when I do. Are there any other stats you want me to look at while I'm at it?

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The reason I asked is the GOM doesn't change as the result of a cell swap, at least not right away. The dealership has to reset the BMS during a cell swap to reset the GOM, which you didn't do. But even though the GOM doesn't change, the pack should drain much slower on account of the better cells. So you might swap packs and see "30" on the GOM... but then drive the car 60 miles. So you can't rely on GOM and gids and such until the BMS has had a chance to re-learn... only driving the car will really tell you the situation.


IFIRC, the Leaf balances batteries by putting a shunt resistor between cells during charging and discharging, which can accommodate small differences in cell capacity within a pack. However, if the cell difference gets too large, then you see something like this:
https://www.dropbox.com/s/tre68n125b99a57/2014-08-16-13-32-20.jpg
(from http://www.mynissanleaf.com/viewtopic.php?f=27&t=7022&start=760#p383786 )

Here's a discussion about imbalanced cells
http://www.mynissanleaf.com/viewtopic.php?f=9&t=17676&start=10

If the replacement cell you got was stronger than the rest of your cells by a large amount, no biggie. You're just wasting some capacity on that cell. But if that cell is weaker than the rest of your pack, you're wasting the remaining capacity of the entire pack when the one cell hits low voltage cutoff, which could be a ton of energy (miles).

Keep in mind that the initial charge (voltage) of that cell isn't critical. The BMS will eventually, over a few charge-discharge cycles be able to balance it back into line during charging using the shunt resistors. Ideally, you should have stuck that one cell on a lipo charger and charged it to the same voltage of the rest of the pack, but the BMS has resolved that now.

What really does matter is if that cell's capacity is significantly less than the rest. If so, it will be artificially limiting your range because once that cell falls below the low voltage cutoff, the entire car will shut down. You should see that in the LeafSpy--measure the difference in mv in all the cells at full charge, drive to near turtle (-- to 2 miles on GOM) and then recheck individual cell voltages with LeafSpy. If you see one cell that's significantly lower than the rest, this is significantly hurting your range. Replacing just that one cell with a better cell could significantly increase your range.

In fact, I suspect this is where Nissan gets a lot of the refurbished packs from for Japan--it's well documented that the center cells in the pack heat up more and thus deteriorate faster than the outside cells. By just replacing the center cells you can dramatically increase the pack capacity. Since Nissan has gotten a lot of batteries back during pack swaps, they likely have a lot of good cells (and a lot of bad ones too).

Sent you a DM with my phone # if you want to talk more.

Lothsahn said:

If the replacement cell you got was stronger than the rest of your cells by a large amount, no biggie.

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That cell was stronger and it seems the car is doing just fine. I don't drive it often, but from what I hear it's working just fine and the range and increased dramatically. We can take it anywhere in town and back (we live about 8 miles from the edge of town) and it's perfectly usable. It doesn't have as much range as our 2015 Leaf but not by much.

The car works well, no issues. Although we have sunk a bit more into the car than we'd like, it's great now.

You mentioned your car only got 25 miles in real world use. Were you thinking of doing something similar to what we've done?

Keefeollers said:

You mentioned your car only got 25 miles in real world use. Were you thinking of doing something similar to what we've done?

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I bought a car very much like yours--bad battery, great car, great price. My original plan was to drive the car until it got under 20 miles range, at which point it would no longer work for us, then plop $5500 on a new battery from Nissan. Nissan has now raised the price to $8000, which has frustrated me greatly.

I have very little mechanical skill, but the short answer is yes, I'm absolutely thinking of doing what you've done. I hate to trash an otherwise good car at 70k miles just because the battery is gone, but spending $8k is insane. If I could get a refurbished battery from the Japanese program OR if I could spend $8k to get a new 40 kwh battery, I would do that in a heartbeat. But $8k for a 24 kwh battery just seems like too much. Spending $3k and a few hours of my time sounds very reasonable, but I'm no mechanic and 400v honestly scares me a bit.

On a plus side, I could recover the existing battery to provide whole-house battery backup in the event of a power outage for a solar system.

Btw, what state do you live in?

Lothsahn said:

Keefeollers said:

You mentioned your car only got 25 miles in real world use. Were you thinking of doing something similar to what we've done?

Click to expand...

I bought a car very much like yours--bad battery, great car, great price. My original plan was to drive the car until it got under 20 miles range, at which point it would no longer work for us, then plop $5500 on a new battery from Nissan. Nissan has now raised the price to $8000, which has frustrated me greatly.

I have very little mechanical skill, but the short answer is yes, I'm absolutely thinking of doing what you've done. I hate to trash an otherwise good car at 70k miles just because the battery is gone, but spending $8k is insane. If I could get a refurbished battery from the Japanese program OR if I could spend $8k to get a new 40 kwh battery, I would do that in a heartbeat. But $8k for a 24 kwh battery just seems like too much. Spending $3k and a few hours of my time sounds very reasonable, but I'm no mechanic and 400v honestly scares me a bit.

On a plus side, I could recover the existing battery to provide whole-house battery backup in the event of a power outage for a solar system.

Btw, what state do you live in?

Click to expand...

I didn't know Nissan had increased the price so much, dang maybe we did pull ahead. Yeah I would never spend $8k just for a 24kwh battery.

400v should scare you, it can easily kill you. If you know a bit about what you're doing it's not hard to manage but never get too comfortable around it. As far as replacing the battery cells go, you don't need too much mechanical skill. Just common sense and a good tool set. And at least 3 jacks.

The idea about a solar battery backup is actually our plan as well. We just need to get around to adding it to our 10kw solar array.

I'm in Windy Wyoming, which has a dramatic effect on the range depending on which direction the wind is blowing.

Awesome thread.
Thanks for sharing!