🔋Analysis of J1.1 with original battery and with .2 replacement

[Regular]

I wanted to start sharing some findings from analysing the battery and charging data I have collected. Will update this post if I find more that might be of interest.

My motivation was originally just to understand if there were any benefits from my replacement battery, but I ended up having to dig pretty deep in some of the J1.1 data also to understand the difference.

A little background:

• I had the PB+ in my 2023 CT4s replaced in March 2026 with a J1.2 (105 kWh) part. To verify, I asked for the proforma service invoice: Part number was 9J1915590RX and spare parts matches the TSB including the PDCC brackets (although they used the non-PDCC APOS code). Car now has a fibreglass bottom.
• Most of the data is Porsche telemetry data (5 months old battery, 3 months new): Available in EU since September 2025 (data.porsche.com). This was the biggest revelation as it provided a solid and directly comparable foundation for both batteries.
• Supported by Car Scanner recording which usually are higher frequency which is helpful in a few edge cases

And a short conclusion up front on having J1.1 battery replaced with J1.2 a part:

• No functional difference in terms of range or fast charging observed
• 95% SoC is the new 85% SoC
• (Not related to battery type: Improved range as SoH went from 87% to 100%)

Below I'll mainly just dump charts and tables with a few comments:


Net capacity and buffers
Looking at the correlation between SoC Display and SoC "true"* for both batteries:

[C6. CHRGR] SoC True in Car Scanner or BMS_SOC_HiRes in Porsche telemetry. SoC HR in Car Scanner is low-res of SoC true.

Original: SoC_true = 92%*SoC_display + 6%
Replacement: SoC_true = 82%*SoC_display + 6%)

This tells us that the battery capacity is allocated this way:

I believe the % allocated and energy available is slightly higher (~86.6-87.0 kWh) than shown here due to %-rounding and such.


Energy content

Reported Energy content (kWh) vs SoC:

Spread for each battery and between the two batteries due to difference in SoH.


Normalizing Energy to 100% SoH cleans it up:

- Energy normalized back to 100% SoH (Made a separate post on SoH readings for J1.2 BMS)
- Numbers converge on 86.5-87.0 kWh at 100% for both batteries.
- Normalizing to 100% SoC shows a mostly flat curve for the original battery, but not for the replacement?


Non-linear energy/SoC curve for the replacement battery:

- Appears as if new battery reports only 88% of energy at ~0% SoC but converges to 100% at 100% SoC
- Divide by 88%+12%*SoC gives a perfectly linear function

I believe the Energy (kWh) is used by the GOM (range indicator) so it has driver implications. See two options:

1. Intentional to add some buffer at the low end of the charge (do we see it on J1.2?)
2. Mistake in adaptation for J1.1

I'm leaning towards 2. as I doubt Porsche would make the GOM less accurate and because the numbers fit perfectly with max Energy content in the J1.1 implementation (88%).


Fast charging statistics

Below chart shows individual charging sessions as a function of SoC and Battery temperature. Color indicates max charging power indicated by the BMS. Yellow color (and largest point sizes) indicates max (335A). New battery sessions are square, old battery round.

It can be a bit difficult to interpret, but there does not appear to be any difference in fast charging performance.

• Max charging power remains ~270 kW (335 A)
• Lowest temperature for max continous power I have achieved with the new battery 32C@8% SoC

Mostly as expected? As I understand it, most of the temp/SoC charging improvements are from the new heater. No improvements in peak from beefier bus-bars, but there are probably more constraints?

I don't have data for more than one proper fast charging session with the old battery so I'm not sure exactly where the temperature cutoffs are on the J1.1.


Will add more details around charging later, for now here is link to two sessions with charging limits, temps, etc.:
DC session (new batt.)
DC Session (old batt.)

AC Charging
Maybe not the most interesting, but here is a typical AC charging session.

• 22kW on-board charger (OBC)
• EU: so 3 phase 230V/400V @ 32A

Charger is in a parking garage with 25-50 public chargers that are power limited in the morning when all are in use. Limit is then increased during the day as demand drops off.

Shown is power into OBC and into the battery - and their ratio (efficiency):

Mapping efficiency as function of the power draw of the OBC (4 dates):

For the 22kW OBC ~95% efficiency @ >10-11 kW, but drops quickly at low power levels
(It's typical that efficiency drops below nominal power, so may be different for the 11kW)

Let me know if you have any questions. Will add more, just need time to process and collect.

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[Leccy61]

Very interesting.

So does this indicate that while the j1.2 battery is likely to be far less prone to failure and therefore a provides a great outcome for a J1.1 owner, Porsche are withholding other benefits such as buffering an additional 10% of capacity and throttling charging speed? Any indication about other j1.2 battery benefits like the more linear relationship between available power and SoC and temperatures?

Intriguing to see if Porsche is really so reluctant to continuously improve their cars other than through new versions or there are technical reasons for all of this.

 

[Regular]

Very interesting.

So does this indicate that while the j1.2 battery is likely to be far less prone to failure and therefore a provides a great outcome for a J1.1 owner, Porsche are withholding other benefits such as buffering an additional 10% of capacity and throttling charging speed? Any indication about other j1.2 battery benefits like the more linear relationship between available power and SoC and temperatures?

Intriguing to see if Porsche is really so reluctant to continuously improve their cars other than through new versions or there are technical reasons for all of this.

Yes. I believe the stated reason was due to homologation, but it seems a bit mad. Although, if the BMS suddenly decides to release some of the capacity as the SoH drops, I'll take it.

I think most of the lower DC charging temperature requirement is actually only lower starting temperature? Basically, that the J1.2 has a much more powerful heater so it is able to "catch up" with the temperature curve.

 

[hrtlik]

Holy F. So they put bigger capacity in but they cap it. Obviously there is no legislation hurdle as there are a lot of upgrades of original Nissan Leaf or BMW i3 and people are happy with it. I just cannot stand this brand anymore.

 

[Regular]

Maybe not the most interesting, but here is a typical AC charging session.

• 22kW on-board charger (OBC)
• EU: so 3 phase 230V/400V @ 32A

Charger is in a parking garage with 25-50 public chargers that are power limited in the morning when all are in use. Limit is then increased during the day as demand drops off.

Shown is power into OBC and into the battery - and their ratio (efficiency):

Mapping efficiency as function of the power draw of the OBC (4 dates):

For the 22kW OBC ~95% efficiency @ >10-11 kW, but drops quickly at low power levels
(It's typical that efficiency drops below nominal power, so may be different for the 11kW)

 

[EXOTIC3]

Can you force them to put a new battery in in 20’ turbo?
I’ve had the red ring twice and all I think they’ve done is changed modules

 

[prj]

If the top buffer is accurate you can charge the new battery always to 100% and have the extra range that way.

 

[snstevens]

OP - You have inspired me!

I’ve known a few “gearheads” in my time, but I think you may be the first official “volthead” of my acquaintance. Keep up the good work!

 

[Midlifecrisis]

So is there no way to unlock the additional capacity? Haw crazy. I think Tesla used to have a bigger battery than advertised with more cells becoming available as the battery aged thereby giving the impression of slower degradation. Maybe this will happen. Or maybe it will remain forever locked away until an aftermarket solution unlocks it after the warranty has ended.

Is the battery weight the same? Or is it heavier with the extra capacity?

 

[Leccy61]

J1.2 battery is lighter than j1.1. 10% less weight, but 10% more capacity (roughly speaking), nice upgrade.

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