Once again...the battery...

[Vim Schrotnock]

Step 2 is unnecessary, and in fact the rebalancing will NOT start if it is plugged in. I'm not sure about the 100% charge balancing, but according to what was communicated to me, it definitely won't hurt to let it sit at 100%. Here's what I do:

1. run the car until it is 15-20% and let it sit overnight. The cells will rebalance at a low state of charge
2. in the morning, plug it in for a few hours before I leave for work.
3. when I return, charge it to 100% and let it sit overnight. Now the cells are rebalancing at a high state of charge.
4. repeat every few months.

From what I was told, having the car sit without charging at a very low charge, and at 100% will allow balancing at the extremes that it typically doesn't see.

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[WattTurbo]

Step 2 is unnecessary, and in fact the rebalancing will NOT start if it is plugged in. I'm not sure about the 100% charge balancing, but according to what was communicated to me, it definitely won't hurt to let it sit at 100%. Here's what I do:

1. run the car until it is 15-20% and let it sit overnight. The cells will rebalance at a low state of charge
2. in the morning, plug it in for a few hours before I leave for work.
3. when I return, charge it to 100% and let it sit overnight. Now the cells are rebalancing at a high state of charge.
4. repeat every few months.

From what I was told, having the car sit without charging at a very low charge, and at 100% will allow balancing at the extremes that it typically doesn't see.

I did step #1 above, but for #2, I drove out to a L3 EA charger. Did the tech say it has to be a L2 for the rebalancing to work? I wouldn't think so because it's done overnight while the SOC is low (10-15%). The reason I asked is because in a previous post, I think you said the tech instructed you to charge to 100% using a L2 EVSE.

 

[WasserGKuehlt]

I did step #1 above, but for #2, I drove out to a L3 EA charger. Did the tech say it has to be a L2 for the rebalancing to work? I wouldn't think so because it's done overnight while the SOC is low (10-15%). The reason I asked is because in a previous post, I think you said the tech instructed you to charge to 100% using a L2 EVSE.

The way I interpreted the advice is that low SoC/floor balancing happens at idle, while middle/top balancing happens while charging. Also, that one must follow the low balancing with that of the top (think sorting by two keys). L3 is “charge asap” so probably minimal if any balancing.

 

[WattTurbo]

The way I interpreted the advice is that low SoC/floor balancing happens at idle, while middle/top balancing happens while charging. Also, that one must follow the low balancing with that of the top (think sorting by two keys). L3 is “charge asap” so probably minimal if any balancing.

ok, that sounds like a reasonable explanation ?

 

[Tooney]

Step 2 is unnecessary, and in fact the rebalancing will NOT start if it is plugged in. I'm not sure about the 100% charge balancing, but according to what was communicated to me, it definitely won't hurt to let it sit at 100%. Here's what I do:

1. run the car until it is 15-20% and let it sit overnight. The cells will rebalance at a low state of charge
2. in the morning, plug it in for a few hours before I leave for work.
3. when I return, charge it to 100% and let it sit overnight. Now the cells are rebalancing at a high state of charge.
4. repeat every few months.

From what I was told, having the car sit without charging at a very low charge, and at 100% will allow balancing at the extremes that it typically doesn't see.

If this is a good idea, I don't understand why it isn't formally communicated to Taycan owners, either in the owner's manual or in a TSB for dealers to share.
The 2022 e-tron training guide, quoted in a post referenced above, says that battery cell group balancing and individual cell balancing only occur if SoC is at least 30%.
This recommended balancing procedure does not make sense to me.

 

[Scandinavian]

If this is a good idea, I don't understand why it isn't formally communicated to Taycan owners, either in the owner's manual or in a TSB for dealers to share.
The 2022 e-tron training guide, quoted in a post referenced above, says that battery cell group balancing and individual cell balancing only occur if SoC is at least 30%.
This recommended balancing procedure does not make sense to me.

Maybe there are two different elements to this procedure.

One is as you say that the manual and the Audi document state, that cell balancing occurs when charging above 30%. So cell balancing will be done all the time when charging

The second element would be the recalibration of the BMS, so that it learns the proper high and low levels of the battery. Then I can understand it needs to go low to 10% and sit there for a while, as well as charge to 100% and sit there for some time.

By doing it as outlined by the advice @Vim Schrotnock got, you combine both procedures??

 

[Sace]

Maybe there are two different elements to this procedure.

One is as you say that the manual and the Audi document state, that cell balancing occurs when charging above 30%. So cell balancing will be done all the time when charging

The second element would be the recalibration of the BMS, so that it learns the proper high and low levels of the battery. Then I can understand it needs to go low to 10% and sit there for a while, as well as charge to 100% and sit there for some time.

By doing it as outlined by the advice @Vim Schrotnock got, you combine both procedures??

Cell balancing happens when the charge level is above 30% - Not while charging. When you charge all cells are charged simultaneously. In order for the BMS to asses the voltage of the cells the battery needs to be resting. It can then discharge the cells individually until they are balanced as shown in the diagram of that document.

The process outlined still makes sense though. The balancing part is just only happening when it's fully charged. I think you are right about it being as much about calibration as it is about balancing.

Let's be honest, cell balancing has been a thing in all multicell batteries for many years so it's hard to imagine that they got this part so wrong that it actually breaks the battery.

Cells dying prematurely is probably the real issue - When they reach the point where the BMS no longer can keep them balanced the car will throw an error.

 

[Vim Schrotnock]

I'll just restate what the Porsche Battery Technician told me so we're clear on the specific Porsche battery rebalancing. There is no rebalancing unless the car is in the 'idle' mode - (car is off and not charging), and it takes several hours to do a proper rebalancing - this the reason to let the car sit, disconnected from the charger, overnight. The BMS system will balance the cells at whatever the charge level is.

For a 100% charge, the battery will charge until the highest charge cell is fully charged, and will discharge until the lowest charge cell is 'empty'. This means if the cells are at different voltages, charging the battery to 100% will only charge the highest charging cell to 100% - all other cells will be somewhat lower. Similarly, the battery will discharge until the lowest charge cell is 'empty', meaning all the other cells will still have some charge.

Balancing of the cells will insure that a fully charged battery has the highest charge in all cells at the maximum charge, and will discharge to the minimum level of all cells when fully discharged.

 

[D00notD00d]

I really, really hope it's not something we should need to think about.

Ideally, fully qualified engineers at Porsche will have actually thought about this (hopefully more than a quick natter over a cup of tea) ....... and will not be leaving it to some banana brained noggin from Manchester, who left school with 1 qualification in woodwork (me) and his rag tag cohorts on a global Internet forum (you lot) to remedy. ?

But you may well be right!

The relative cost of replacing all 28/33 modules vs. 1 or 2 means that financial considerations would trump engineer recommendations. Holding stock of old and new parts also doesn’t seem viable.
Does anyone know how ‘unused contingency’ storage is configured? Spare modules/spare cells? And if the spare status is visible via an OBD scanner?

 

[Vim Schrotnock]

So far, very happy with the new battery. SOH 99+%, all cells balanced to within .003V at all SOC. Indicated range is some 10+% higher than I've ever had.

 

[j.w.s]

I do not have inside knowledge about the Porsche battery management system specifically. But I do build lithium batteries, and in doing so commonly start out with not-quite-balanced battery packs, and I have a technique that may apply to the Taycan.

The Battery Management System (BMS) has a "balancer" function to bring each of the cells in a pack to the same voltage. It does this by drawing current from the highest voltage cell and stuffing it into the lowest voltage cell until they are all at the same voltage. But there are limits to this process:
1) It only starts when the battery is fairly full but not entirely full. Balancing generally DOES NOT happen at low states of charge. The exact start voltage is a configuration item, but balancing might start at 80% or 90% charge and it might or might not end before the pack is at 100%.
2) The amount of current that the balancer can draw from a battery is typically VERY limited. It works nicely to keep a well balanced pack fully balanced, but the current is likely too low to bring a not well balanced pack into proper balance under typical conditions.

Because of the above, balancing your pack might best be done by:
1) Draining the car to say 70%
2) Charging up to 95-100% at a VERY low rate so that you give the balancer plenty of time to work. As in charge at 1KW or even less, not your typical 9.6KW to 19KW.
3) Repeating a few times if the voltages don't fully converge.

The above said, your pack is only ~0.01 voltage off of balance, which I doubt would itself cause any type of error to be thrown, much less one with "death" in its nickname. I would guess that your problems are worse than just a slightly off balance battery pack.

By the way, I take back what I said above. That is called "top balancing" and it appears that Porsche instead does "bottom balancing". With top balancing the BMS works to equalize cell voltages when the battery is nearly fully charged. With bottom balancing the BMS works to equalize cell voltages when the battery is nearly fully discharged.
So the way to let the Taycan balance the pack is to discharge the battery quite a bit, to say 10%, and then let it sit there NOT charging for quite some time - typically many many hours to a few days depending on the level of imbalance and the capacity of the balancer.

 

[Tooney]

Interesting to me that suggestions here to balance the HV battery and/or calibrate the BMS

- reduce SoC to 10-15% and increase SoC to 100% and let Taycan remain uncharged at those charge levels for extended periods.​

​

conflict with owner manual charging instructions:

Use the timer function to program a high-voltage battery charge state of approx. 80 % for daily use of the vehicle without any long-distance driving. ​

When the charge state is below 5 %, connect the vehicle to the power grid following operation and charge the high-voltage battery. ​

If required, a battery charge of 100% can be programmed before starting long journeys.​

At ambient temperatures above 86 °F (30 °C), connect the vehicle to the power grid following operation and charge the high-voltage battery with alternating current (AC) to a maximum charge state of 85%. Use the timer function.​

A couple of possibilities:
- Following owner manual charging instructions to charge to 80% for normal daily use does not result in HV battery balancing and BMS calibration (unless owners do these undocumented 10% and 100% methods).
Taycan owner manual instructions (and published TSBs) omit procedures needed for proper battery balancing and BMS calibration.

- Following owner manual charging instructions does accomplish battery balancing and BMS calibration.

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