Hey Guys I wanted to share an experience we had with my wife's new BYD Atto 3 at only 44,000 KM (60kWh battery) that started to happen since 3 months ago that we noticed super slow DC charging speeds.

we do regular trips to Bangkok every month, and my last 2 trips were a NIGHTMARE! Drive on highway for 2 hours (110-120kmh) and charge for 2 hours, the whole 800km trip took me 15 hours. I wanted to blow up this expensive POS out of rage.

It started 3 months ago.

The Issue

DC fast-charging performance has degraded significantly. On standard 180kW PTT (EV Station PluZ) units, no other car plugged in in the PTT EV HUB, where I previously hit a sustained 88kW curve up to 60% SoC, I am now seeing a very hard throttle always.

• My observed Rate: 36–42kW when starting at 10% or 20% SoC.

• Dropping as low as 30kW at 37% SoC.

The "Smoking Gun"

As an computer engineer, I’ve been monitoring the pack's thermal behavior via my OBD and CarScanner.

During the most recent 30kW throttle event, the data revealed a massive internal thermal imbalance:

• Max Cell Temp: 50.0°C (The BMS hard-throttle threshold for LFP) Cells 9,10,11

• Min Cell Temp: 33.0°C (cells at the beginning of the pack)

• Cell Delta: 17.0°C (massive)

• Inlet Water Temp: 41.0°C (ambient Temperature 31C)

My Engineering Analysis: A 17°C delta across a liquid-cooled pack is a major anomaly. In a normally functional battery system, the coolant loop should maintain a delta of <5°C. The fact that the water is at 41°C while specific cells are hitting 50°C suggests a failure in the heat exchange coefficient—likely a clogged coolant manifold or a malfunctioning active chiller (refrigerant-to-glycol heat exchange).

Now, the most strange SOH Degradation Jump:

Beyond the charging speed, I’ve noticed a non-linear drop in State of Health (SOH) that doesn't align with standard cycle wear of LFP batteries:

• Nov 2025: 95.26% SOH

• Dec 2025: 94.52% SOH (-0.74%)

• Feb 2026: 93.00% SOH (-1.52%)

• Delta: -2.26% in 3 months / ~5,000km. WHAT THE HECK!!!

This massive cliff in SOH, combined with the thermal delta, says that the overheating cells are dragging down the average health of the entire pack, or the BMS is recalibrating the SOH based on the internal resistance of certain cells.

In summary: it's now a 56kWh battery after 44,000 km and 3 years.

Dealer Response

Took the car to BYD today after after showing all the data, the only action they could do was a BMS Firmware Upgrade. which they just did.

While a BMS update might adjust the thermal fan curves, it cannot fix a 17°C physical temperature delta. If there is air in the lines, a dead pump, or a blocked channel, the software will eventually hit the same 50°C ceiling. I told them this and they cant do anything else.

I’m monitoring now to see if the update simply hides the symptoms or if it actually triggers more aggressive cooling.

Anyone else seeing these massive cell deltas or SOH jumps on low-mileage Atto 3s?

The good news: Wife is ok to upgrade to a 800V EV car by next year. Let's see December motorshow. I think the G6 at 1.2MB is a total bargain, but the 7X is absolute beast only in my dreams.

The BMS update didnt change anything, maximum DC fast charging speed I get is 30-44kW maximum.

The battery started ok, then raised to 50C very quickly.

The other thing I realized, the maximum discharge power has been reduced from 165kW to 115kW, that's the maximum I can accelerate now.

I guess going back to the dealer to fight with them.

Today, second time I dropped the car I insisted to check the cooling pipes and pump because they didn't do it yesterday.

The engineer found the pump coolant level was 500 , which should be 1100.

I can't charge to test since none available, so let's see tomorrow.

the car is fully back to like it was before. No cell overheating and low speed dc charging.

My key take aways in this nightmare:

• The engineers at BYD can be a bit clueless and very arrogant to listen. Don't want to listen, they said my battery has 100 cells, that this is normal and Thailand is hot. I had to fight with them and push them to do what Gemini insisted: the cooling pipes and pump.

• The staff ladies and are really nice and patient, they even let me borrow the Dolphin to go home and back (60km round trip) specially because no taxis here. So they're awesome, and super kind. Never an issue in communication.

The engineers are arrogant idiots. Even when they realize they've been wrong all the time, and still act like that. They refuse to accept the car had a problem where it clearly had a serious problem.

I think no more BYD for me, even the amazing sealion7 as a great car, but anything goes wrong your car become a liability.

Why this is a serious (from Gemini):

• If the coolant level is at 500 (likely ml in the reservoir or a proprietary level sensor value where 1100 is the nominal set point), your cooling loop is effectively cavitating.

• Thermal Mass: it lack the necessary volume of glycol to absorb the heat flux from the Blade cells during high-C rate charging ($>$1C).

• Air Locks: At that low level, the pump is likely pulling air. This creates "dry spots" in the battery cold plate. This perfectly explains the 17°C cell delta—the cells near the inlet might get a trickle of coolant, while the "far" cells are sitting in stagnant air pockets, rapidly hitting that 50°C ceiling.

• The 115kW Discharge Limit: This is "Limp Mode" lite. The BMS has detected that it cannot safely reject heat during high-load discharge. It has slashed peak power from 150kW (165kW peak) to 115kW to prevent the hot cells from hitting the thermal runaway or accelerated degradation threshold ($>$55°C) while driving.

• Potential Failure Points: Usually this leak occurs at the O-rings, the Expansion Valve (EXV) that manages battery cooling, or the Chiller itself.

• Compressor Risk: The refrigerant also carries the PAG oil that lubricates the compressor. Running at 500g puts the AC compressor at risk of seizing due to lack of lubrication.

What I still need to so that didn't do test is a full system pressure to find out of there's a leak, otherwise the gas will leak again. They didn't do this!!!

Some feedback based on my knowledge/research/googling regarding the Atto 3 and my personal OBD monitoring with my OBD device and CarScannerPro app over approx 2.5 years and 65,000km...I got my Atto 3 in late Oct 2023 and I think it was around Jan 2024 that I started monitoring OBD data a lot. I leave the OBD dongle plugged in all the time and very frequently monitor the data real time with the CarScanner app, while I'm fast or slow charging, car turned off, etc.

Anyway, the Atto 3 Extended Range 60.48KWH model using 126 blade battery cells separated. Although all 126 cells are placed side by side (no separate modules) there are 10 BMS daughter boards with each daughter board monitoring either 14 cells or 12 cells. Specifically, the boards span 12 and 14 sets of cells (3x 14s boards and 7x 12s boards) with one temperature probe for each of the 12 or 14 cells....there is not a temperate probe for each and every 126 cells. However, each and every cell's "voltage" level is monitored. So in a round about way the "temperature" is monitored like a multiple module battery pack (although it's not really)...with each pack consisting of 12 or 14 cells.

Where you show 11 battery modules/packs are you sure about that? My Atto in CarScanner only shows 10 packs which matches up with what my internet research shows. Maybe in the modification of your CarScanner dashboard you have mislabeled some readout boxes.

To confirm how many packs you actually have go to the CarScanner menu while you have a connection between the car and app and then select "All Sensors." This will show you all the possible OBD readings/data elements the OBD dongle and CarScanner app can "possibly" read. Now scroll to where it list the BASU Pack numbers. It should show the "possibility" of reading from 13 total packs (if an EV had 13 modules) but in the case of the Atto only 10 of 13 will show temperature and voltage readings since there are only 10 packs... Pack 11-13 in the app will not reflect any readings. Or at least that all my Atto shows (i.e., 10 packs) and what my research showed for a Extended Range 60.48KWH battery pack.

Regarding cooling of the battery pack it use A/C refrigerant (R134A) and not glycol. The glycol is used to cool the motor and electronics setting on top of the motor like the OnBoard Charger, Power Drive Unit, Invertor, etc. There is a small chiller which is sometimes used to help cool the glycol although the radiator does the bulk of the glycol cooling.

Pack 1 is closest to the engine...the front of the car and Pack 10 at the rear. When driving the packs in the front half will heat up first (especially packs 1-3) probably since they are closest the heat given off by the drive motor and the further back packs heat-up last as you drive along or are charging assuming active cooling in not underway yet....that is, the battery pack cooling system allowing full flow of R134 refrigerant thru the battery pack cooling plate with the front part of the cooling plate always cooling down first, cooling to the lowest temperature since the refrigerant starts warming up/absorbing heat as it travels thru the 8 cooling channels/tubes on the cooling plate. Four channels carry the refrigerant down to the end of the battery (pack 10) where the refrigerant does a U-turn at a manifold assembly and then flows back up the battery pack past pack 1 to the battery refrigerant outlet.

In all my OBD monitoring while driving and fast/slow charging the biggest battery pack differential I have seen is approx 13C where Pack 1 was at around 29C and Pack 10 at 42C. I'm pretty sure no pack has never exceeded 42C before the refrigerant cooling slowly brought it back down into the 35-38C ballpark. And getting to 42C doesn't occur often...usually only in the hottest weather and extended high speed driving. During the cooler part of the year the highest temp I've seen the battery pack reach is around around 38 or 39C with extended high speed driving.

The A/C system in the Atto 3 uses 1100grams of R-134a refrigerant....it cools both the cabin and battery. Since the BYD technician said he measured only around 500 then that means the system lost quite a bit of coolant....had a small leak and he topped up the refrigerant to the full level of 1100grams. Had you noticed decreased "cabin" cooling also?

Regarding the SOH, the CarScanner app shows a "calculated SOH" which means it's not reading a direct SOH data element from the BMS but is making a guess by using the "HV Pack Pack Factory Capacity" data element (151AH in your case) and "HV Battery Pack Factory Nominal Capacity (140.43AH) in your case...in the image you posted above. Both of these OBD elements can be read directly and not calculated. That "Nominal Capacity" is determined by the BMS on a "periodic" basis...yes, the BMS does a capacity test/recalibration. When the battery was "brand new" the BMS did a Nominal Capacity determined what the capacity was and I'm sure it was less than 151AH. It was probably in the 145 to 146AH actual range when brand new. Why not 151AH since you have 151Ah blade cells, well, once all the cells are connected together, BMS daughter boards connected, and other stuff hung on like a relays it can't provide the full capacity of individual, standalone cells.

Now my CarScanner says my Atto battery pack has 152AH cells (the car blade battery comes in variations of 150 to 152Ah) and when brand need it showed "Nominal Capacity" of 145.73Ah....so, I'm taking that to be the actual SOH of my battery pack when it was brand new...just born....a 100% SOH. Just a few days ago I did a 3 to 100% charge which happened to trigger one of the BMS periodic "Nominal Capacity" updates....it now shows 139.84Ah. So, using 145.73AH as my reference point when the battery was brand new (a.k.a., SOH) and dividing that into 139.84AH I get a current SOH of health of 96% which sounds about right for a LFP battery pack after almost 2.5 years and 65,000km,

HOWEVER, BUT if used 152AH divided into the BMS determined current "Nominal Capacity" I would get a sad 92% SOH...this is how the Carscanner app "calculates/guesstimates the current SOH since it can not directly read SOH nor does it know what the battery pack "actual/nominal" capacity was when brand new if the BMS has done at least one new capacity determination. The app's SOH reading is a guesstimate to make customers happy since they want to see some kind of SOH reading even if it's not that accurate.

In my opinion/testing, if a person knows what their original "HV Battery Pack Factory Nominal Capacity" was when they first got the car (which I do know mine was most likely 145.73Ah) then using that original capacity AH number to calculate current capacity will give a more accurate SOH.

So, in your case "if, repeat, if" your original Nominal Capacity was say 145.73AH like mine was and your current Nominal Capacity shows around 140.43AH then your battery pack current SOH is actually around 96.6% vs 93%.

Cheers

Below weblink provides good info on the BYD Atto 3 Extended Range 60.48KWH battery. And his multiple Youtube videos (he did a half dozen or so videos) during the battery disassembly to turn it into a home solar system battery. And the Dolphin and Seal batteries are basically the same design although I think the Seal has a better battery cooling plate that uses a "serpentine" cooling channel pattern to route the refrigerant thru the plate vs the straight pattern used on the Atto and Dolphin batteries.

https://forums.aeva.asn.au/viewtopic.php?t=8323

23 hours ago, Pib said:

Below weblink provides good info on the BYD Atto 3 Extended Range 60.48KWH battery. And his multiple Youtube videos (he did a half dozen or so videos) during the battery disassembly to turn it into a home solar system battery. And the Dolphin and Seal batteries are basically the same design although I think the Seal has a better battery cooling plate that uses a "serpentine" cooling channel pattern to route the refrigerant thru the plate vs the straight pattern used on the Atto and Dolphin batteries.

https://forums.aeva.asn.au/viewtopic.php?t=8323

Thanks a lot for the info! Greatly appreciated, even Gemini dont tell me this much details. I've always been a lazy engineer.

So, I have the logs in CarScanner since wife got her atto3 in the beginning, the logs should have the original capacity.

The issue I had was really serious because the last cells at the end reached 50C quite often and one time when I drove hard to test it, it went to 52-54C and my total discharge capacity dropped to 116kW from the usual 286kW that car scanner shows.

I'm monitoring everyday, and I am really happy now that I can fully charge at 88kW every day.

15 minutes ago, brfsa2 said:

So, I have the logs in CarScanner since wife got her atto3 in the beginning, the logs should have the original capacity.

The oldest data I could for [BASU] HV Battery Pack Current Nominal Capacity (Ah)

• 1xx.00 (2023/08/08 new car)

• 146.47 (2025/04/24) (-1.0%-2.0%)

• 143.85 (2025/11/07) (-1.8%)

• 142.72 (2025/12/09) (-0.8%)

• 140.43 (2025/12/25) (-1.6%)

• 140.43 (2026/02/24)

• 140.43 (2026/03/29)

• 140.43 (Today )

My SOH degraded really fast in 2025 mostly end of year not in Summer time. driving 3000 KM a month on Average.

During ownership, DC Fast charge have been occasional, 2-8 times a month at most, and mostly at 56kW.

2 hours ago, brfsa2 said:

The oldest data I could for [BASU] HV Battery Pack Current Nominal Capacity (Ah)

• 1xx.00 (2023/08/08 new car)

• 146.47 (2025/04/24) (-1.0%-2.0%)

• 143.85 (2025/11/07) (-1.8%)

• 142.72 (2025/12/09) (-0.8%)

• 140.43 (2025/12/25) (-1.6%)

• 140.43 (2026/02/24)

• 140.43 (2026/03/29)

• 140.43 (Today )

My SOH degraded really fast in 2025 mostly end of year not in Summer time. driving 3000 KM a month on Average.

During ownership, DC Fast charge have been occasional, 2-8 times a month at most, and mostly at 56kW.

My SOH / HV Battery Pack Factory Nominal Capacity readings in CarScanner never changed from late Oct 2023 *when I first got the Atto) to around 30 Jun 2025....around 19 months later....it was always at 145.73 Ah for those 19 months. So, I assumed from the title of the "HV Battery Pack Factory Nominal Capacity" that this was the actual/BMS calculated capacity where the battery pack was first born "and it would that reading done at the factory would never change"....thought that for 19 months. Then a mid 2025 BYD OTA update changed that belief.

On 30 Jun 2025 when an OTA for the Atto installed where the version went for 1.8.0 to 1.10.1 (latter is still the latest version) I noticed CarScanner now reflected a new SOH percentage because the "HV Battery Pack Factory Nominal Capacity" reading had changed to 142.33 Ah. That BYD OTA update had apparently triggered the BMS to update/test current battery Nominal Capacity.

Now since my Atto updated to OTA 1.10.1, I have seen one more BMS update where the "Nominal Capacity" changed from 142.33 Ah to 139.84 Ah on 4 Apr 2026....which was 10 months after it's last "Nominal Capacity" udate. I now thought to myself it sure appears the OTA 1.10.1 update may now force the BMS to update more "periodically"....or maybe it updated BMS instructions to from never doing a capacity update unless it was accomplished at a BYD dealership with special equipment "to" just update periodically without being forced at a BYD dealership. As to how often "periodically" is such as every X-amount of kilometers, X-amount of charges, etc., I've been unable to figure that out.

I've never been able to figure out what triggers a SOH / HV Battery Pack Factory Nominal Capacity update since it don't happen often and I haven't detected any pattern like after X-amount of kilometers, X-amount of below 10% to 100% charges to recalibrate the BMS range remaining/percent of charge remaining guess-o-meter, etc...etc....etc.

Around every 3-6 months (closer to 3 months) I do a "less than 10% to 100% charge as recommend by the BYD manual to recalibrate the BMS/range remaining guess-o-meter and except for twos time there was never a change in SOH. I've probably done this 10 times so far. However, as already talked the SOH has only updated 2 times.

Basically, the SOH update / battery capacity update is "sticky"....below is what Google AI says about "sticky" BMS SOH updates:

Google AI

"Sticky" Battery Management System (BMS) State of Health (SOH) updates in electric vehicles refer to a common phenomenon where the reported health percentage of a battery remains unchanged for long periods, or changes very slowly despite degradation or heavy usage. This occurs because SOH is an estimated value rather than a directly measured one, and algorithms often prioritize stability to prevent user anxiety, relying on slow-acting, long-term trends. [1, 2, 3]

Key Reasons for Sticky SOH Updates:

• Estimation Delay: The BMS calculates SOH based on complex algorithms, aging models, and cycle counting, which may only update periodically (e.g., after certain charge cycles).

• Range Anxiety Mitigation: Manufacturers often tune BMS software to avoid jumping percentages, which could lead to service requests. The reported "range" or SOH can sometimes seem "sticky" for weeks or months, needing specific usage patterns to force an update.

• Need for Calibration: SOH calculations can get "stuck" if the car is rarely charged to 100% or rarely driven to a low State of Charge (SOC).

• BMS Updates/Resets: When a BMS receives a software update or a hard reset (e.g., following a recall), the SOH reading can be reset to a default, often appearing "healthier" than it is, before taking several deep discharge cycles to show a realistic, lower value.

How to "Unstick" or Update SOH:

• Deep Cycles: Performing multiple charge cycles that go below 20% and up to 100% can help the BMS re-calibrate.

• OBDII Diagnostics: Using external tools (like OBDII dongles with apps such as Car Scanner) can sometimes provide a more direct, current reading of the battery's health compared to the display.

• Software Upgrades: Service updates for the BMS can address "sticky" behaviors and improve the accuracy of SOH reporting.

3 hours ago, brfsa2 said:

The oldest data I could for [BASU] HV Battery Pack Current Nominal Capacity (Ah)

• 1xx.00 (2023/08/08 new car)

• 146.47 (2025/04/24) (-1.0%-2.0%)

• 143.85 (2025/11/07) (-1.8%)

• 142.72 (2025/12/09) (-0.8%)

• 140.43 (2025/12/25) (-1.6%)

• 140.43 (2026/02/24)

• 140.43 (2026/03/29)

• 140.43 (Today )

My SOH degraded really fast in 2025 mostly end of year not in Summer time. driving 3000 KM a month on Average.

During ownership, DC Fast charge have been occasional, 2-8 times a month at most, and mostly at 56kW.

If I was you, I would go with the 146.47 Ah as being your new born battery "HV Battery Pack Nominal Capacity" and then use that in your math to determine current SOH. Ex: 143.43 Ah current capacity divided by the brand new capacity 146.47 Ah which gives a 97.9% SOH.

Don't use the CarScanner "calculated" SOH reading which uses the 151 AH capacity in your case as the new born battery pack capacity for the reference/starting capacity.

I was wondering why some of your CarScanner Dashboard reading titles were different from mine like the battery capacity title....I think I figured it out....see my comments on top of the snapshots below which are from my CarScanner/for my Atto.

On my CarScanner dashboard it's called

HV Battery Pack "Factory" Nominal Capacity and not

HV Battery Pack "Current" Nominal Capacity like on your CarScanner dashboard.

HOWEVER, in the CarScanner "Sensors" area which the dashboard readings pull their data from/are linked to

and also pull their title from (although you can edit the title later) when first creating a dashboard reading

it has changed at some point since I first started using from using "Factory" to "Current." This change probably happened due to a

CarScanner update OR maybe a BYD OTA update changed the name. Anyway, it now explains to me why some of your dashboard titles were different from mine...probably because I started using the CarScanner before you....and maybe you retitled a few of the readings to more layman's terms. Now I know if the title in the Sensor area gets updated/changed it probably will not updated/change the name in the Dashboard....a person would need to recreate that one dashboard readings or just manually change the dashboard title.

4 hours ago, Pib said:

I was wondering why some of your CarScanner Dashboard reading titles were different from mine like the battery capacity title....I think I figured it out....see my comments on top of the snapshots below which are from my CarScanner/for my Atto.

On my CarScanner dashboard it's called

HV Battery Pack "Factory" Nominal Capacity and not

HV Battery Pack "Current" Nominal Capacity like on your CarScanner dashboard.

HOWEVER, in the CarScanner "Sensors" area which the dashboard readings pull their data from/are linked to

and also pull their title from (although you can edit the title later) when first creating a dashboard reading

it has changed at some point since I first started using from using "Factory" to "Current." This change probably happened due to a

CarScanner update OR maybe a BYD OTA update changed the name. Anyway, it now explains to me why some of your dashboard titles were different from mine...probably because I started using the CarScanner before you....and maybe you retitled a few of the readings to more layman's terms. Now I know if the title in the Sensor area gets updated/changed it probably will not updated/change the name in the Dashboard....a person would need to recreate that one dashboard readings or just manually change the dashboard title.

I only have these showing up. the Current nominal capacity has been stuck like that for months. I have done AC full charges to 100% at home. lately I can only charge at PTT Fast charge, I'm only getting 190V at night here. welcome to the country side single phase infrastructure. :D

On 4/7/2026 at 9:03 PM, brfsa2 said:

I only have these showing up. the Current nominal capacity has been stuck like that for months. I have done AC full charges to 100% at home. lately I can only charge at PTT Fast charge, I'm only getting 190V at night here. welcome to the country side single phase infrastructure. :D

It's only showing a limited number (6 in this case) because you have a "Hv battery" entered as the filter search term. When I tried it with the "Hv battery" term you had entered I got the same showing as you.

Try again without any search term (just a blank entry) and "many" sensors will appear....many pages of sensors with each page showing around 11 possible sensor readings....probably around 200 individual possible reads. The majority of the sensors readings relate to the battery, but there are many others not related to the battery and don't appear in the "starter" dashboard....you need to add these to the dashboard if wanting to monitor them easily.

One sensor reading I added to my dashboard was the [ABS] Master Cylinder Pressure reading which shows pressure being applied to the disc brakes. When monitoring this reading it quickly makes perfect sense why brake pads/rotors last a lot longer on EV than ICE cars because although a person may conservatively press the brake pedal to slow down why driving unless you were stopping very aggressively/slam the brakes the pressure level will stay at zero (i.e., no fluid pressure actually being applied) because it's actually the drive motor(s) that is braking the EV as the drive motor instantly switched from being a motor consuming energy to a generator creating energy....that generation of energy causes a varying braking force. Only when you get down to around 15kmh speed does regen braking not work anymore and brake hydraulic pressure will always be used as normal. Yeap, seeing when hydraulic brake pressure is "actually" applied when pressing the brake pedal in an EV quickly made it perfectly clear to me as to why EV brake pads/rotors last a long, long, long time.....the brake sensor reading (picture) while driving was worth a thousand words.

And although many sensors will appear some may not have an reading showing until you tap this once or twice as they may only update until you create a dashboard entry for them or you tap them while looking at them in the Sensor page.....and other will not show any reading. The ones that will show readings are the sensors that the OBD adapter and CarScanner can actually communicate with. And the ones the adapter & app can communicate with/give readings are the ones you might want to add to your app's dashboard in order to view quickly/easily without needing to go to the Sensors page.

When you first install CarScanner it comes with X-amount of prebuilt dashboard pages...it kinda like just a "starter dashboard." You can then add more pages/sensors/reading to the dashboard. Now the free version of CarScanner has limitations in building/expanding the dashboard but CarScannerPro which costs around Bt150 to upgrade to thru Google Play/Apple Store removes those limitations...gets rid of all advertising...etc.

A good article on protecting and charging an Atto 3 in "hot" regions like the Middle East, Southeast Asia, etc.

https://www.bydaccessories.store/blogs/news/byd-atto-3-battery-temperature-protecting-extreme-heat

As I'm thinking of getting an EV - I found this whole thread a valuable read.

My own experience of AC systems in ICE cars and at home is that losing the gas is a common issue, probably due to leaking seals in the compressor. And as the battery cooling system in the BYD is basically an automotive AC system, gas leaks may be quite likely, especially in older cars. It also sounds like overheating of the batteries can be a serious issue.

So do the cars not have a warning system when the gas has leaked to a critical level? Dropping from 1100 grams to 500 sounds like a serious leak, but there was no automatic warning on the dash?