High voltage battery charges a flat 12v battery??

[Sonny1980]

Hi everyone,

Just found this forum while searching online. I've read quite a few topics about flat 12v batteries but I think none of them actually answers this question.

I didn't drive my 2011 Auris HSD for 3 weeks, since mid December until just a few days ago, so with very cold days and negative temperatures during the night, I guess it's normal the 12v Battery went flat?

Anyway, when I tried to drive the car, I had the usual symptoms: all lights on the dash would come on except for Ready and P, and the engine wouldn't start. I tried several times for about 40 minutes, turning the ignition on/off, sometimes leaving it on for several minutes hoping for the engine to come alive, no luck. I called the AA and, while I was waiting, I decided to try again and suddenly Ready and P also lit up and the engine started!!

Was I just lucky or does this mean that if the 12v Battery is flat, if we turn on the ignition, the high voltage Battery will start charging it? Because if it's not the case, I would expect that the more I tried, the more it would discharge the 12v battery? Considering that at first I even had the headlights and interior lights on, etc...

After a long drive, I've had no issues since. But just in case I want to check the battery voltage. What's the best app to check it?

Thanks!

 

[Gerg]

52 minutes ago, Sonny1980 said:

Was I just lucky or does this mean that if the 12v battery is flat, if we turn on the ignition, the high voltage battery will start charging it?

The car will start to charge the 12v Battery when the car is 'ready', that's to say, when it is ready to drive away.  But not with the ignition simply switched 'on' (in the 'accessory' position).

To get the car into the 'ready' state, the car must boot the computer, pressurise the brake booster (a motor noise you hear every start-up, and also in normal use) and operate the contactor.

Your Battery was too flat to do those last two parts successfully, I suspect. But only just.  I suspect that with having a light load on the Battery (i.e. ignition on, but not managing to properly start), it has probably lightly warmed the battery plates etc. - enough to manage to just provide sufficient current to perform a normal start-up (which takes, for a brief moment, around 20 amps - a tiny amount by normal car battery start-up demands).

As your battery charge was marginal, you could have achieved the same effect by bringing it indoors to warm it up, say.  Not that I'm suggesting you do that. 

Your battery really needs a prolonged charge, leaving it less than near fully-charged will accelerate its ageing!  How old is it, btw?

As I'm sure you've discovered, the 12v battery does not crank the engine over, that is the job of the traction battery.  So as long as the 12v battery has just enough charge do do it's job, the engine will start with its usual enthusiasm, potentially concealing a near-flat 12v battery.  It's a bit of an Achilles' Heel on these cars.

HTH

[Sonny1980]

Thanks for the reply, Gerg!

Right after that I drove around 50 miles on the motorway. Any idea if this would be enough to charge it back to full?

I've also driven it almost daily but on shorter commutes. Anyway, that's why I want to check through an OBD2 reader what's its voltage before and after starting the engine.

Thanks.

[TonyHSD]

I  believe your 12v Battery hasn’t been dead at first place but for some reason you couldn’t start the car. If the Battery was low it may require to press depress brake pedal twice for the first start up and you perhaps didn’t do that and the car was set only in acc mode with all lights on dashboard illuminated. When you tried second time the car had its second brake press and so started. If you haven’t driven the car for some time 30 min might not be sufficient to recharge the Battery and longer time in ready mode will be beneficial. You can keep the car in ready mode for an hour with all accessories off to rejuvenate your battery or with external smart charger. 

[Sonny1980]

No, I was pressing the brake, as always, so it goes straight to Ready. I was doing that all the times I was trying to get it started. I drove it for about an hour on the motorway on the day that happened. Hopefully was enough to fully charge the Battery.

Thanks!

[Gerg]

Regrettably, it won't have fully charged it.

Contrary to what you know from other cars, it doesn't make any difference to the 12v charge rate whether the car is going fast, slow or even stationary, as long as it's in 'ready' mode.

That's an interesting thought from TonyHSD above!  I hadn't thought of it being 'operator error'!

If you can recharge the Battery with an external charger, perhaps overnight, then at least you know it has reached it's maximum capacity.  You then can establish if the battery's capacity (reduced through ageing!) is still enough for the car to be reliable with your usage pattern.

The car has the capacity on its DC/DC converter (in the inverter) to charge the Battery quite quickly, but it seems that for some reason, it is often quite leisurely in doing this, which is the topic of some ongoing debate, and frustration for too many owners!

Many find out, if they get to measure their Battery voltage at rest, that their car is routinely running around with a part-discharged 12v battery, with no good reason.  The car has deemed this to be 'OK'.

For what it's worth, some of the latest 'smart' battery chargers (e.g. NOCO or CTEK brand) have a 'repair' mode, which can be used to (intelligently) persuade the battery to achieve a slightly higher capacity.  Worth thinking about these, but that repair mode can add up to 6 hours on a charge, and its use is suggested every 12 months. 

[TonyHSD]

21 minutes ago, Sonny1980 said:

No, I was pressing the brake, as always, so it goes straight to Ready. I was doing that all the times I was trying to get it started. I drove it for about an hour on the motorway on the day that happened. Hopefully was enough to fully charge the battery.

Thanks!

Hi, 
sometimes after Battery been low or every time been disconnected and then reconnected or after new Battery replacement the car needs to run initialisation process explained in a link from Toyota that was shared by Aisin in a different post. The car won’t start just by pressing the brake pedal once and push start button., instead the car will only be set in acc mode. You will need to release brake pedal and press again to start the car. I discovered that long time ago by working on these vehicles and disconnecting the 12v Battery negative terminal. Now it’s confirmed by Toyota official document. 
This is very likely what has happened to you. If your battery was dead you wouldn’t be able to unlock the car with the remote., in some cases it will let you unlock but won’t start. Then the dash will behave erratic, and goes dead.  You just had been luck to be able to start, run the car for longer to try to save your battery and you can measure voltage with a volt meter after you switch off and wait 20 min. , or perhaps measure next day before starting and driving. 

[Auris Geezer]

I too have a similar problem.  The car has been in my garage for a week not used, and previously only for short trips since the beginning of December.  Today I go to use it and the dash momentarily lit up with the message of "low 12v battery" and promptly shut off so no lights or messages at all, completely dead.  I have an Oxford trickle charger and it read initially 2.4v and giving it 0.87A, but after about 6 hrs, it's still giving it 0.87A but the voltage is only up to 6.1V.  Do you think it needs a new Battery?

[TonyHSD]

14 minutes ago, Auris Geezer said:

I too have a similar problem.  The car has been in my garage for a week not used, and previously only for short trips since the beginning of December.  Today I go to use it and the dash momentarily lit up with the message of "low 12v battery" and promptly shut off so no lights or messages at all, completely dead.  I have an Oxford trickle charger and it read initially 2.4v and giving it 0.87A, but after about 6 hrs, it's still giving it 0.87A but the voltage is only up to 6.1V.  Do you think it needs a new battery?

Yes it seems like you will need a new Battery. 

[Auris Geezer]

Thanks Tony, should have a new one tomorrow.  As it's lost it's charge and, it'll be disconnected, will I have to reset anything or will anything be "lost" please?

[TonyHSD]

1 hour ago, Auris Geezer said:

Thanks Tony, should have a new one tomorrow.  As it's lost it's charge and, it'll be disconnected, will I have to reset anything or will anything be "lost" please?

Hi Trev,

When you connect the new Battery first goes positive terminal then negative one make sure you have the key fob with you in case the alarm goes off to stop from waking up the whole neighbourhood. Then when you trying to start for a first time the car may not start with single press brake pedal , if so release pedal and press again and then push start button again. Let the car run its cycles and meanwhile you can reset radio stations and audio settings. The daily trip mileage will be reset too and I think that’s all. 
Good luck. 👍

[AisinW]

22 hours ago, Auris Geezer said:

I too have a similar problem.  The car has been in my garage for a week not used, and previously only for short trips since the beginning of December.  Today I go to use it and the dash momentarily lit up with the message of "low 12v battery" and promptly shut off so no lights or messages at all, completely dead.  I have an Oxford trickle charger and it read initially 2.4v and giving it 0.87A, but after about 6 hrs, it's still giving it 0.87A but the voltage is only up to 6.1V.  Do you think it needs a new battery?

Any lead acid Battery that has been discharged below 12V always degrades permanently.  It is called suphation process. The Lead is coated by insulating surface of PbSO4 and it is not reversible.  You may make the Battery back to be useful but will not hold the original capacity.  Very often it drops less than 50% original capacity once the voltage dropped below 12V even for one time incident.  

[loz8]

Sitting in the car in Ready mode,but in Park depletes Traction,the bars go from high to low in about 20 mins and the message comes up telling you why.

[loz8]

Check a poster has had or has the Auris Hybrid,they are a different kettle of fish to other Toyotas.

[AisinW]

1 hour ago, loz8 said:

Sitting in the car in Ready mode,but in Park depletes Traction,the bars go from high to low in about 20 mins and the message comes up telling you why.

It is normal. It takes power to turn the computer on in Ready mode. In P the HV Battery is being charged if the engine is on but not in N. That's the proper way to charge the 12V and HV Battery if it sits more than 2 months for 30 minutes. The 12V Battery is charged by DC/DC converter regardless the engine is on or not, the hybrid battery is at low or high bar. It only depends on the 12V voltage reading. It could be as high as 20 Amps to 0.1 amperage or lower. 

 https://static.nhtsa.gov/odi/tsbs/2021/MC-10190469-9999.pdf

If the HV is too depleted this is an expensive service.  

https://static.nhtsa.gov/odi/tsbs/2022/MC-10213900-9999.pdf

[Derek.w]

I dont expect all Toyota garages to have one of those devices for charging the HV system 

just one on to units in the UK is my guess.

 

[AisinW]

I am not sure about that. In Germany it is not legal turn the car on in Park (for warming the cabin). But I will show this TSB if someone/police ask or try to fine me. I believe turn the car in P in hybrid as part of service does not violate such  law. 

[MagicBoy]

On 1/10/2023 at 2:58 PM, AisinW said:

Any lead acid battery that has been discharged below 12V always degrades permanently.  It is called suphation process. The Lead is coated by insulating surface of PbSO4 and it is not reversible.  You may make the battery back to be useful but will not hold the original capacity.  Very often it drops less than 50% original capacity once the voltage dropped below 12V even for one time incident.  

Keep in mind the Hybrids use an AGM Battery, which are a lot less prone to sulphation and therefore happier being deep cycled.

[AisinW]

6 hours ago, MagicBoy said:

Keep in mind the Hybrids use an AGM battery, which are a lot less prone to sulphation and therefore happier being deep cycled.

Yes, AGM handle better on deeper cycle but the bottom range is still above 12V before it degrades. Generally speaking, it is at about 25%.  The main reason we use AGM in some Toyota is because it is stored inside the cabin. if it is in the engine bay, we do not  need AGM that cost 3-4x more for the same size.   

The reason is not about the performance but safety in case of accident or any leak. Wet cell can harm people/passanger or HV Battery that is often close by. 

[TonyHSD]

Last night checked the hybrid Battery with an app and shoes ok but what I seen about the 12v Battery was not good, resting voltage of 11.8v . Perhaps should be prepared to replace it soon. 

[Corollanutter]

11 hours ago, MagicBoy said:

Keep in mind the Hybrids use an AGM battery, which are a lot less prone to sulphation and therefore happier being deep cycled.

Not all hybrids use the AGM Battery. For example, the Corolla 1.8 uses a conventional Battery (mounted under the bonnet) whereas the 2.0 Corolla uses an AGM Battery (mounted in the side luggage area). 

[MagicBoy]

5 hours ago, Corollanutter said:

Not all hybrids use the AGM battery. For example, the Corolla 1.8 uses a conventional battery (mounted under the bonnet) whereas the 2.0 Corolla uses an AGM battery (mounted in the side luggage area). 

The question was about an Auris in the Auris section. It's correct for a Mk2 Auris.

[AisinW]

7 hours ago, TonyHSD said:

Last night checked the hybrid battery with an app and shoes ok but what I seen about the 12v battery was not good, resting voltage of 11.8v . Perhaps should be prepared to replace it soon. 

11.8V?  It is possible that you just open the driver door, they key is in ACC mode, or one of the dom light is on. @MagicBoy what  I meant, they are all going bad if discharged below 30% state ~11.8-12V is the limit before permanent damage occurs. 

[TonyHSD]

1 minute ago, AisinW said:

11.8V?  It is possible that you just open the driver door, they key is in ACC mode, or one of the dom light is on. @MagicBoy what  I meant, they are all going bad if discharged below 30% state ~11.8-12V is the limit before permanent damage occurs. 

I was actually keeping the car in acc mode for around 5min trying to connect Carista to a new phone. Perhaps maybe that’s why after connection was established it showed me 11.8v. Then after I started the car showed as usual 14.7v. 

[AisinW]

9 hours ago, TonyHSD said:

I was actually keeping the car in acc mode for around 5min trying to connect Carista to a new phone. Perhaps maybe that’s why after connection was established it showed me 11.8v. Then after I started the car showed as usual 14.7v. 

In ACC mode when connected to Carista OBD2 my Battery only shows 11.7V since 2 years ago.  But if I turn the car off for another 2 minutes and all off, measured with voltmeter from fusebox shows 12.3V. 

The 11.8-12V limit before sulphation is for  open circuit voltage. When the Battery has no load/current flow. 

At high load like when we start the car, 60 Amps is drawn and once the Battery drop below 10V, we usually gets an error code. Typical CEL in Prius 2, it shows transmission code but acutally was a weak  battery.