Roman Catholic :- It's all the driver fault for not not changing the battery. If the driver have change the battery despite no warning , this would not have happen.
                           There's nothing wrong with BYD emergency braking when battery is low and it is acceptable. The fault lies on the driver for not changing the battery.
                           I know more because I manage a fleet of cars. Yes managing a fleet of cars , tells me that BYD emergency braking is not a safety issue and it is a driver issue.  

What diverting idiot ? The fucking 12V lead acid battery has a limited life span. No point writing further to you obviously you don't understand how the whole fucking electrical system works and you say it's irrelevant. I am already managing fleet of vehicles and I will drop smart asses like you in an instant.

Best answer would be that owner to post an update how is his BYD now after his 12V Low Battery was replaced.

This is an EV, we are talking about.

For ICE, my clients are supposed to listen to me when I tell them to replace their batteries. Those who don't listen and when face problems, it's my fault ?

Don't have to reply to that idiot.

The ps is very clear its the battery

Don't understand why issue happen so many plotektor, when we should be pointing finger at the manufacturer

I smell bullshit.

Either BYD Malaysia just wanna keep something more sinister under wraps or BYD system architecture has a serious flaw where a non safety critical fault can trigger system shutdown. Even so, no reason to have car totally unresponsive.

We can only hope our authorities can intervene before something worse happens.

.
Fyi, .......

Gemini AI Overview

Yes, a weak 12V battery can potentially cause door sensors to fail or malfunction. Sensors rely on a consistent and adequate voltage supply to operate correctly. If the battery is weak or failing, it may not provide the necessary voltage for the door sensor to function properly.

Here's why a weak battery can affect door sensors:
- Insufficient Voltage:
Sensors require a specific voltage to operate. A weak battery may not provide enough power, leading to unreliable or inaccurate readings from the sensor.
- Intermittent Operation:
Even if the battery isn't completely dead, it might fluctuate in voltage, causing the sensor to operate intermittently or incorrectly.
- System Malfunction:
A weak battery can also affect other vehicle systems, including the car's computer, which might influence the operation of the door sensors.
- Other Factors:
While a weak battery is a common cause, other factors like wiring issues, sensor failures, or problems with the vehicle's computer can also contribute to sensor problems.

If you're experiencing issues with your car's door sensors, it's always a good idea to have your battery checked and ensure it's providing the necessary voltage. 
.

Even if the battery isn't completely dead, it might fluctuate in voltage, causing the sensor to operate intermittently or incorrectly.

A weak battery can also affect other vehicle systems, including the car's computer, which might influence the operation of the door sensors.

Do a door sensor need to be that sophisticated? What the door sensor use for?

1) door sensor can be just a contact switch. An On/Off signal to the ECU. No electronic require inside. Keep it simple, cheap and failsafe.

2) If there require some crazy electronic stuff inside the switch, the circuit can be design to take wide range of voltage. 10-14.4v is enough to operate and tackle the low/high voltage of the battery. Battery don't drop dead till 0v.

1. TPMS Control Module Malfunction
The TPMS relies on a control module (ECU) to receive and interpret signals from tire sensors.

A weak car battery may cause:

Voltage drops during engine cranking.

Intermittent power supply to the TPMS module.

Faulty initialization of the TPMS system on startup.

This can result in the system failing to recognize one or more tire sensors.

2. Sensor Signal Issues
Some TPMS systems (especially indirect types) depend on stable vehicle electrical systems.

If the battery voltage is low, radio frequency (RF) signals from the tire sensors might not be processed properly, leading to:

Missed sensor readings

False TPMS warnings

3. BCM (Body Control Module) Glitches
TPMS often interacts with the BCM or other vehicle computers.

A weak battery can cause these modules to:

Glitch or reset

Lose stored configurations

Trigger diagnostic trouble codes (DTCs)

These issues can mimic or cause TPMS failures.

4. Startup Sequence Disruption
When starting the car with a weak battery, voltage may dip below the required threshold for proper ECU function.

This can interrupt the initial communication handshake between the TPMS control unit and tire sensors.

5. Battery Disconnect History
If the weak battery has recently been disconnected or replaced:

Some TPMS systems need to be reinitialized or relearned.

If this process wasn’t completed, the system may continue to display faults or fail to recognize sensor IDs.

. Incomplete Combustion and Poor Engine Operation
A weak battery can cause poor spark plug performance or weak ignition, especially during startup.

This leads to incomplete combustion, potentially causing:

Increased carbon monoxide (CO) emissions

Rough idling and engine misfires

If there's a leak in the exhaust system or poor ventilation (e.g., idling in a closed garage), carbon monoxide could enter the cabin.
➡️ Carbon monoxide exposure is a major cause of headaches and can be life-threatening.

🌬️ 2. HVAC and Ventilation System Malfunction
Some modern cars use electrical actuators for air recirculation and ventilation.

A weak battery may cause:

Blower fan issues

Stuck air recirculation flaps

Reduced fresh air flow

This can lead to stale air, higher CO₂ buildup, or inadequate cabin ventilation, which may trigger headaches, especially on longer drives.

⚠️ 3. Electronic Glitches and Stress
A weak battery can cause unpredictable electrical behavior:

Dash warnings

Radio or infotainment malfunctions

Flickering lights

This can increase driver stress or anxiety, which is a common headache trigger.

🚗 4. Cabin Air Quality Degradation
A weak battery may reduce the performance of systems that support:

Cabin air filters

Air ionizers or purifiers (in luxury vehicles)

This can let in more pollutants or allergens, which can cause sinus headaches or migraines in sensitive individuals.

🧠 Summary
A weak battery won’t directly cause headaches, but it can indirectly contribute by:

Leading to carbon monoxide exposure

Reducing ventilation quality

Causing vehicle stress or malfunctions

1. Poor Cabin Lighting and Instrument Visibility
A weak battery can cause:

Dim dashboard lights

Flickering displays

Inconsistent interior lighting

This can strain your eyes, especially in low-light driving conditions or at night. Straining to see instruments or road signs can cause:

Blurry vision

Eye fatigue

Temporary visual discomfort

💨 2. Faulty HVAC and Ventilation (Dry Eyes)
Battery-related issues can affect the HVAC system:

Weak fan motors

Non-functioning defogger or heater

Poor humidity control

This can lead to:

Dry eyes from low humidity or stale air

Foggy windshield making you squint or strain more

Dry or irritated eyes can temporarily reduce visual clarity and comfort.

🧠 3. Headaches and Fatigue (Perceived Eye Problems)
As mentioned earlier, a weak battery can cause:

Cabin air quality issues

Increased CO or CO₂ exposure (from poor combustion or poor ventilation)

Stress from warning lights and malfunctions

These can lead to:

Headaches

Brain fog

Fatigue

All of which can feel like poor eyesight when it’s actually more about cognitive and visual processing fatigue.

🔌 4. Flickering or Unstable Screens
Infotainment systems and HUDs may flicker or reset with low voltage.

Eye strain can come from trying to read a flickering screen or adjusting constantly to unstable lighting.

❗ If You’re Concerned About Your Eyesight
If you're noticing visual symptoms while driving, don’t ignore it — especially if accompanied by:

Dizziness

Nausea

Lightheadedness

A feeling of pressure behind the eyes

Also rule out:

Carbon monoxide exposure (very serious)

Underlying vision issues that worsen in low light or high contrast

.
Are you saying an EV car's weak or failing 12V battery will not cause it's door sensors,  "starter" function, comfort functions, control units and actuators to fail.? .......

https://www.varta-automotive.com/knowledge/...the-12v-battery - Electric vehicles and the 12V battery
Let's have a look at the many different xEVs on the market and the role of the 12V battery inside all of them.
.... And technically speaking, one could still call it a starter battery for "electric cars". When the vehicle is parked, the high-voltage battery is disconnected from the electrical system for safety reasons. If the journey is to be continued, the high-voltage battery must first be started - and it is precisely this starting process that is initiated by the 12V battery.

The vehicle's 12V network supplies comfort functions, control units, sensors and actuators. ...

Remember, in the original thread about this BYD incident, the initial diagnosis by the BYD SC was 12V battery fault. Today, Sime Darby says it's door sensor fault. The two could be very related, ie ...
12V battery fault ---> door sensor fault ---> the original BYD incident.
.

Are you saying an EV car's weak or failing 12V battery will not cause it's door sensors,  "starter" function, comfort functions, control units and actuators to fail.? ......

https://www.varta-automotive.com/knowledge/...the-12v-battery - Electric vehicles and the 12V battery
Let's have a look at the many different xEVs on the market and the role of the 12V battery inside all of them.
[color=green] .... And technically speaking, one could still call it a starter battery for "electric cars". When the vehicle is parked, the high-voltage battery is disconnected from the electrical system for safety reasons. If the journey is to be continued, the high-voltage battery must first be started - and it is precisely this starting process that is initiated by the 12V battery.

Remember, in the original thread about this BYD incident, the initial diagnosis by the BYD SC was 12V battery fault. Today, Sime Darby says it's door sensor fault. The two could be very related, ie ...
12V battery fault ---> door sensor fault ---> the original BYD incident.

https://forum.lowyat.net/index.php?showtopi...ost&p=111589177
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Above repost fyi, ie if the 10 month old/20,000km 12V battery is weak, it  can fail while the BYD Atto 3 is being driven on the highway until  the BIG battery has <20% charge , even though the car had been started earlier by the weak 12V battery.
.

Above repost fyi, ie if the 10 month old/20,000km 12V battery is weak, it  can fail while the BYD Atto 3 is being driven on the highway until  the BIG battery has <20% charge , even though the car had been started earlier by the weak 12V battery.

.
From your geekzone forum link on page 2, .......

arthurgeek:

One or two BYD Atto 3 owners have mentioned in FB posts that, if the main battery falls to a state of charge of less than 15%, the 12V battery will no longer be topped up by the main battery. 

If this is true, it might pay owners to make sure the main battery is immediately charged up once it gets to a SOC of less than 15%. Can anyone confirm whether EVs stop charging the 12V battery when the SOC of the main battery drops to quite a low level.


Obraik:

A Tesla will. Once the main pack gets low (I can't remember the exact number, but it's very low) it will stop maintaining the 12v/15v battery and it will warn that if you leave the car that it might not start again if you don't charge it.

= it seems, even when being driven (= eg EV car not being charged at home), the 12V battery will not be charged by the BIG battery when the latter has <15%-20% charge.

Gemini  AI Overview

Yes, the 12V battery in a BYD Atto 3 can fail while driving, though it's not necessarily the primary cause of sudden braking issues reported by some owners. A low 12V voltage can potentially cause the vehicle to stall or experience other power-related problems. 
.

= it seems, even when being driven (= eg EV car not being charged at home), the 12V battery will not be charged by the BIG battery when the latter has <15%-20% charge.

A Tesla will. Once the main pack gets low (I can't remember the exact number, but it's very low) it will stop maintaining the 12v/15v battery and it will warn that if you leave the car that it might not start again if you don't charge it. [/color]

One or two BYD Atto 3 owners have mentioned in FB posts that, if the main battery falls to a state of charge of less than 15%, the 12V battery will no longer be topped up by the main battery. 

If this is true, it might pay owners to make sure the main battery is immediately charged up once it gets to a SOC of less than 15%. Can anyone confirm whether EVs stop charging the 12V battery when the SOC of the main battery drops to quite a low level.

.
No. Where does it says it was being parked.?

Where does the whole thread say it is about jumpstarting the 12V battery after BYD Atto 3 cars broke down while being parked and not while being driven.?

Fyi, .......

https://evpowerhouse.com.au/blog/byd-atto-3...ems-and-issues/ - Common BYD Atto 3 Problems and Issues - 29 Dec 2023
.... Power failure issue

Some owners have experienced a terrifying situation – the car suddenly losing power with no warning. The culprit? A depleted starter battery with a critically low voltage reading. While a simple recharge solved the immediate issue, concerns remain about customer support’s handling of battery replacement options. ...

.... Owners have also noticed the 12V battery draining more quickly, particularly when the main traction battery has a low charge. While the exact cause remains under investigation, these two issues could be pointing towards a potential problem with the car’s electrical system. ...

12V battery issue

Frequent complete discharges of the 12V battery, leaving the car stranded, are a recurring problem. While trickle charging offers a temporary fix, the battery quickly drains again. Owners are seeking information about the 12V battery’s charging cycle in EVs and when it receives a top-up from the main battery. ...
.

No. Where does it says it was being parked.?

[i]I’m one of the small but significant number of Atto 3 owners who’s had a 12V battery failure out of the blue.  I was able to get going immediately with a lithium jump starter and my dealer swapped the battery out that day, so no major issue, but it has generated considerable noise and speculation on the Atto FB pages both here and Australia, and other EVs have a similar problem so it’s not isolated to BYD.


After investing in a battery monitor I think we have four key root causes working together:


The 12V battery in an EV is small (low Ah rating) as it doesn’t need to deliver cranking amps to a starter motor.  Anything to save weight in an EV is a good thing, but it means there’s not a lot of reserve capacity
There is a constant current draw even when the car is turned off just to keep the comms and sensors running.  In particular I’ve noticed there is a heavier than normal draw when the charging cable is plugged in waiting for a scheduled charging session to start.  There seems to be significant interaction between the car’s BMS and the EVSE over this period
While in transit from China some batteries have degraded.  Yet some unfortunate owners still have problems after their battery has been replaced
The BMS is not aggressive enough in checking the state of the 12V battery and recharging it from the traction battery.  BYD are releasing a firmware fix for this issue in early February.  This will increase the frequency of checks and top-ups, but doesn’t mention whether the low voltage threshold (around 11.5V) will be changed.  In ICE-land a battery reading under 12V is suspect, but EVs with their lighter current draw may be able to get away with a lower voltage threshold in normal use.
BYD also claim there is a compatibility issue between the Atto and some EVSEs.  This doesn’t ring true to me, but I have little evidence either way.  In my case I have a Wallbox Pulsar which is recommended by BYD dealers, yet I still had a problem.


So my recommendation to EV owners is to keep a lithium jump starter handy.  They are much more convenient than jumper leads from another car, and they’ll start an ICE too.  Not a lot of point checking the battery as in normal use it will range from 12.6V after charging to 11.5V after a period of inactivity.
Operationally, don’t keep the charging cable plugged in unused for long periods, and minimise other battery demand, eg by keeping the key fob well away from the car when parked.
[/I]

.
AFAIK, that thread says the 12V battery in BYD Atto 3 cars could fail while parked or while being driven = breakdowns. From your geekzone forum link, .......

arthurgeek

I then found that there have been a lot of breakdowns due to 12V battery failures in the new BYD Atto 3, which arrived in NZ around August 2022. Some members of a FB group have reported that the battery management system (BMS) of the Atto 3 has not been adequately charging the 12V battery and just about every day an owner reports that their Atto has broken down due to the 12V battery failing. Apparently BYD has explained that when the vehicles were being freighted to NZ the batteries discharged to lower than expected levels and that the BMS couldn't recharge the batteries back to full capacity. The BMS is apparently being upgraded to check the 12V battery more often and charge it up for double the amount of time, and an OTA is due out soon.

So, do all EVs have problems with keeping the 12V battery fully charged, and if so, what are the main reasons why this is happening? Should EV owners invest in a battery charger and a jump-starter and check the state of charge of the 12V battery regularly?

SteveNXZ

.... The BMS is not aggressive enough in checking the state of the 12V battery and recharging it from the traction battery.  BYD are releasing a firmware fix for this issue in early February.  This will increase the frequency of checks and top-ups, but doesn’t mention whether the low voltage threshold (around 11.5V) will be changed. ... 

Gemini AI Overview

The traction battery charges the 12V battery in electric vehicles when the 12V battery voltage drops below a certain threshold. This typically occurs when the car is not plugged in and parked for a few days, or when the 12V battery is not being adequately recharged by regenerative braking.  The Hybrid/EV Powertrain control module (HPCM2) monitors the 12V battery and will initiate a "battery maintenance" mode to charge it if necessary. 

Please address the points raised by my evpowerhouse link above.
.

Please address the points raised by my evpowerhouse link above.

AFAIK, that thread says the 12V battery in BYD Atto 3 cars could fail while parked or while being driven = breakdowns. From your geekzone forum link, ......

b]SteveNXZ[/b]

.... The BMS is not aggressive enough in checking the state of the 12V battery and recharging it from the traction battery.  BYD are releasing a firmware fix for this issue in early February.  This will increase the frequency of checks and top-ups, but doesn’t mention whether the low voltage threshold (around 11.5V) will be changed. ...  [/color]

Isn't the above article statement self-explanatory, ie a terrifying situation like an emergency brake from 100km/h in 6 sec due to low 12V battery.?

AFAIK, the traction battery recharges the 12V battery periodically whenever the BMS detects the latter has low voltage, eg <11.5V, whether the EV car is parked or is parked and being charged or is being driven, ie not only when parked. Your claim has no computer logic, ie your claim that the BMS does not periodically check the 12V battery for low voltage and recharges it when needed while being driven. .......

Gemini AI Overview

While driving an EV, the auxiliary battery directly powers the headlights, climate control system, and sensors. This battery is also known as a 12-volt battery, according to the Department of Energy (DOE). The main traction battery powers the electric motor, while the auxiliary battery handles the accessories. 

More similar info saying 12V battery directly powers accessories while driving, not the traction battery, .......

https://www.reddit.com/r/electricvehicles/c..._all_the_stuff/ - Is there a separate battery for all the stuff that a normal car battery uses electric for?  - 8 months ago
lucky1pierre

I've seen a few posts recently that have got me thinking - my EV has what looks like a traditional battery under the bonnet. I've assumed that this is for things like windows, lights, screens etc and that the battery pack under the vehicle is for power only.

Is this accurate or am I wildly missing the mark here? Does the battery pack supply absolutely everything?

(104 comments)
.

Some owners have experienced a terrifying situation – the car suddenly losing power with no warning. The culprit? A depleted starter battery with a critically low voltage reading. While a simple recharge solved the immediate issue, concerns remain about customer support’s handling of battery replacement options. ...

Isn't the above article statement self-explanatory, ie a terrifying situation like an emergency brake from 100km/h in 6 sec due to low 12V battery.?

lurkingaround claims:- The phrase "terrifying situation" in the article means an emergency brake from 100km/h in 6s

AFAIK, the traction battery recharges the 12V battery periodically whenever the BMS detects the latter has low voltage, eg <11.5V, whether the EV car is parked or is parked and being charged or is being driven, ie not only when parked. Your claim has no computer logic, ie your claim that the BMS does not periodically check the 12V battery for low voltage and recharges it when needed while being driven. .......

lurkingaround claims:- The traction battery recharges the 12V battery "periodically" when the BMS detects low voltage for both parked and driving.

https://forum.lowyat.net/topic/5521715
Above repost of the original incident which is quite similar to that descibed as a "TERRIFYING SITUATION" in my evpowerhouse link, ie power failure  with no warning due to faulty 12V battery ---> door sensor malfunction ---> computer falsely sensed doors as open while driving ---> auto activation of EPB and power shutdown.

.
AFAIK, what you have shown above is for normal operation of an EV car with a normal 12V battery, ie not for abnormal operation and/or with a weak (eg old) or failing 12V battery.
....... The 12V battery has a normal life span of only about 1 year(.?).

Eg if driving at night in the dead of winter (below 0*C) with the headlights on and heaters at full blast, the normal 12V battery's voltage would definitely drop below 11.5V due to heavy load or power draw = requires heavy recharging by the traction battery = EV car range drop by 30% to 50%. .......

And from your geekzone forum link, ie one BYD Atto 3 car breaking down per day due to failing 12V battery caused by an abnormally long ship-freight from CCP China to NZ, .......

arthurgeek

I then found that there have been a lot of breakdowns due to 12V battery failures in the new BYD Atto 3, which arrived in NZ around August 2022. Some members of a FB group have reported that the battery management system (BMS) of the Atto 3 has not been adequately charging the 12V battery and just about every day an owner reports that their Atto has broken down due to the 12V battery failing. Apparently BYD has explained that when the vehicles were being freighted to NZ the batteries discharged to lower than expected levels and that the BMS couldn't recharge the batteries back to full capacity. The BMS is apparently being upgraded to check the 12V battery more often and charge it up for double the amount of time, and an OTA is due out soon.
.

Above repost of the original incident which is quite similar to that descibed as a "TERRIFYING SITUATION" in my evpowerhouse link, ie power failure  with no warning due to faulty 12V battery ---> door sensor malfunction ---> computer falsely sensed doors as open while driving ---> auto activation of EPB and power shutdown.

lurkingaround claims:- The terrifying situation in evpowerhouse link is similar to the powerfailure with no warning due to faulty 12V battery which caused door sensor malfunction which caused computer falsed sensed door as open.

AFAIK, what you have shown above is for normal operation of an EV car with a normal 12V battery, ie not for abnormal operation and/or with a weak (eg old) or failing 12V battery.
....... The 12V battery has a normal life span of only about 1 year(.?).

lurkingaround claims:- The traction battery recharges the 12V battery "periodically" when the BMS detects low voltage for both parked and driving.

lurkingaround says: Eg if driving at night in the dead of winter (below 0*C) with the headlights on and heaters at full blast, the normal 12V battery's voltage would definitely drop below 11.5V due to heavy load or power draw = requires heavy recharging by the traction battery = EV car range drop by 30% to 50%. .......

And from your geekzone forum link, ie one BYD Atto 3 car breaking down per day due to failing 12V battery caused by an abnormally long ship-freight from CCP China to NZ, .......