Strange calibration issue on gen2 Max Pack - service has not seen this before

[kxev]

There is the real possibility this is a bug in Rivians secret reservation they do. My Gen 1 large stops increasing range at 97%.

it seems Rivian sets aside a buffer so that as a battery degrades it didn’t show in the range until a certain degradation amount has happened.

Yeah, it seems like it's related to that "secret reservation."

As my battery has degraded (based on drain test measurements), that reserved amount seems to have gone UP. Which doesn't make sense, I would expect the opposite...it should make its way down to zero and then main pack capacity should finally drop.

It really seems like there are some logic errors around how they calculate that reservation.

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[mkhuffman]

Yeah, it seems like it's related to that "secret reservation."

As my battery has degraded (based on drain test measurements), that reserved amount seems to have gone UP. Which doesn't make sense, I would expect the opposite...it should make its way down to zero and then main pack capacity should finally drop.

It really seems like there are some logic errors around how they calculate that reservation.

Maybe, but it also might be related to the BMS and how it estimates the SoC.

As the cells age, I expect some will degrade faster than others. And maybe when they are charging quickly, they get out of sync and there are many that are fully charged, and many that are not.

So the BMS incorrectly reports the total pack charge at 99% when really there are a lot of cells still charging. That makes more sense to me than a "secret reservation" issue.

I think Rivian developed the BMS, and maybe they didn't spend enough time on this use case. I wish I still had my Mach-e so I could compare. I do remember my MME spent a lot of time at 99%. But not as long. I chalked it up to battery size but maybe it is a BMS issue. That's my vote.

 

[kxev]

As the cells age, I expect some will degrade faster than others. And maybe when they are charging quickly, they get out of sync and there are many that are fully charged, and many that are not.

So the BMS incorrectly reports the total pack charge at 99% when really there are a lot of cells still charging. That makes more sense to me than a "secret reservation" issue.

I think Rivian developed the BMS, and maybe they didn't spend enough time on this use case. I wish I still had my Mach-e so I could compare. I do remember my MME spent a lot of time at 99%. But not as long. I chalked it up to battery size but maybe it is a BMS issue. That's my vote.

One question I have is how fast the vehicle can actually charge when balancing. I thought it was pretty limited, maybe 15 - 20kW max, or possibly < 11kW matching L2 speeds (I see the vehicle hang out at 7 - 10kW for 10 -15 minutes at the very end, and a Rivian tech also told me that's the normal time and not 30+ mins.) I believe there are some bleed resistors that can run in parallel with higher-voltage modules, but all that requires much lower current. (I don't know how pack balancing works in detail at all, maybe someone can correct me on this.)

So it doesn't make sense that my pack is balancing cells when it's at 86kW. Vs just charging normally but it shows a % that's too high.

Your logic makes sense if it can indeed charge faster. Maybe the problem is something like it hits "99%" when the highest cell is at X.X volts (but then like you said, there are a lot of cells still charging.) But it's supposed to hit "99%" when the lowest cell is at X.X volts, to allow for energy to come in via balancing.

There can still be a "secret reservation" even given this. All that is describing is any capacity past 140kWh on a Max Pack, irrespective if it came in via balancing or not. The effect you describe could be leading to that reservation amount appearing to be off.

My old Y was ~22% degraded, but it was much more graceful than this. Rated range on the dash gradually declined over time, from 330 miles to 258 miles. The amount of time it spent at 99%, balancing cells, also went up significantly...but the total power (kWh) it added after "99%" never went up. The %s stayed consistent, and nav estimates also stayed accurate (just less range as it degraded, as expected.)

 

[kxev]

Hit a new peak, 107kW at "99%"!

This was my first fast charge with 2026.03, as well. So this confirms that the bug is still present.

 

[Bumble1978]

Ok you said 2 minutes 10 minutes ago...

Flattest curve ever

 

[Bumble1978]

Confirmed ..25 minutes at 99% and still going I'd say the bug is plausible, yes?!?

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[Bumble1978]

FWIW, as soon as I hit stop within seconds it changed to

 

[kxev]

FWIW, as soon as I hit stop within seconds it changed to

Thanks for testing! This confirms that gen1 Max Pack is affected in the same way as gen2. (I assumed this was the case, since Rivian told me it affects "all Max Packs", but it's nice to confirm.)

I don't think you hit true 100%. If I unplug before it stops on its own, it'll flip to "100%" if it was above ~99.5% SoC (not sure that's the exact threshold and it's not necessarily just a rounding effect, but it's around there.) Though you definitely came close. But if you let it keep charging, it'll continue to balance and more kWh will become available until it stops on its own.

My own gen2 R1S Dual Max Performance has now been returned to Rivian, and I'm enjoying the used gen1 R1T Quad Large I bought to replace it. Fast charging works as expected, it flips from 99% to 100% in less than 5 minutes. Range estimates have been quite accurate, too! Over 1000 miles road tripped so far, and none of the % loss that I saw on my Max Pack.

I'll be curious to see if Rivian finally fixes the Max Pack bug in the next update.

 

[Bumble1978]

Guess there was a reason I never charged to 100% - just didn't know why lol other than I didn't really ever need to even on a road trip from WA to UT and back again.

 

[mkhuffman]

Guess there was a reason I never charged to 100% - just didn't know why lol other than I didn't really ever need to even on a road trip from WA to UT and back again.

Charging to 100% every so often is important for the BMS to be calibrated properly. It needs some 100% to 10% cycles to accurately estimate the top and bottom of the pack.

 

[Bumble1978]

@mkhuffman Meant to say never charge to on road trips using DCFC because of the time suck in general past 70ish. Definitely charge to at home often preparing to leave.

To be fair Jordi was probably overdue for a deep calibration charge. Rarely gets that low as my Lady is usually the person who daily's the truck so 70%-50% maybe 35-40% if she has meetings in different locations outside the office.

 

[Bumble1978]

FWIW seems to be a lower end issue too...just did the drive from Everett to Spokane via I-90. It was projecting a 7% arrival the entire way until just before we got to Moses Lake where I had just seen it drop the arrival SOC from 7% to 5% about 5-10 minutes before Moses Lake. Spidey senses kicked in and I added Moses Lake SC at about 35%. Quickly grabbed sustenance at the Lep-re- kon Market, charged to about 45, new projection was only 41% needed to make it to Spokane with about 25% left. Kept watching the arrival SOC drop and got in with 9%.

L2 charging to on the hotel's Tesla Destination stations. So we'll see how it goes on the way back in a few days.

 

[kxev]

FWIW seems to be a lower end issue too...just did the drive from Everett to Spokane via I-90. It was projecting a 7% arrival the entire way until just before we got to Moses Lake where I had just seen it drop the arrival SOC from 7% to 5% about 5-10 minutes before Moses Lake. Spidey senses kicked in and I added Moses Lake SC at about 35%. Quickly grabbed sustenance at the Lep-re- kon Market, charged to about 45, new projection was only 41% needed to make it to Spokane with about 25% left. Kept watching the arrival SOC drop and got in with 9%.

Yeah, the issue affects the whole charge curve. My vehicle had the same pattern, the % loss would get worse at low SoC. I suspect there is some logic where SoC gets adjusted down when the vehicle notices voltage is lower than expected, and this happens more at low SoC.

Good call on topping off! I started either using a 20 - 25% arrival estimate, or slowly charging to true 100% (that's the only time I'd trust the Max Pack with a 10% estimate.)

 

[mkhuffman]

Yeah, the issue affects the whole charge curve. My vehicle had the same pattern, the % loss would get worse at low SoC. I suspect there is some logic where SoC gets adjusted down when the vehicle notices voltage is lower than expected, and this happens more at low SoC.

Good call on topping off! I started either using a 20 - 25% arrival estimate, or slowly charging to true 100% (that's the only time I'd trust the Max Pack with a 10% estimate.)

I also had a low charge dramatic drop last weekend when I did a 400 mile (round trip) highway drive. I did one DCF charge on the way home and the estimated arrival was 15% SoC, but I arrived with 5%. Efficiency was much worse than normal also, so maybe it isn't the same issue. But it was the first time it has been off by that much.

Usually the estimate is very accurate. For example, I did a 340-mile trip (two hotels stays and mostly highway, but slower traffic) and arrived back home this morning. It predicted arriving at home at 11%. I arrived at home with 12% SoC. Interestingly, this trip only included some L2 destination charging and no DCFC, so maybe it is related. For both trips I charged to 100% at home prior to leaving.

 

[JeremyP]

I had a similar situation coming home after lots of fast charging during a spring break trip from Colorado to Southern California. Our last charge stop was in Blanding, Utah before getting back to Grand Junction and I charged until an estimated 20% remaining at arrival. It was down to a 15% arrival estimate by Moab and I arrived home with 5%.

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