12v Battery Dead

[LordByronUK]

And low and behold the 12v Battery on our 2016 NX FSport is now dead and got it replaced by the AA today (£165). We thought it had just run low because of low usage of late, but turned out the thing was on its last legs and just wasn't holding charge and needed to be replaced. Quite surprising for a 4 year old vehicle...What was interesting is that the new 12v Battery may have slightly improved fuel economy. I noticed immediately that the hybrid Battery wasn't having to be topped up as much when low, as the hybrid Battery is used to top up the 12v Battery. The AA guy even said that when the car detects the 12v is low (when idle or in slow traffic), the car will top up the hybrid Battery more often to keep the 12v topped up, and the manual even said something similar if I remember. I was sitting in the car stationary for about 20 minutes on lowest 2 bar charge and even then it didn't need to top up the hybrid system once. Managed to get 47mpg from a good mixed drive after 30 minutes with the new Battery, which is definitely higher then what I usually get on that route. Could be a coincidence, I'll have to see what our average is like after a few more tanks of driving to be sure though.

It does make sense that a dying 12v can put a drain on the hybrid system. Anyone else experienced this?

[Steve Oliver]

I have to say the system intrigues me. I have a 2019 NX 300h - and I have an AA Car Genie fitted, which under normal circumstances monitors the car for faults - and on my previous car, a diesel Nissan X-Trail, it would happily tell me that my 12v Battery had good charge for weeks on end. Now that the Genie is in my NX, it regularly a day or so after using the car, tells me that the 12v Battery is low on charge and could do with a drive to charge it up. I have on a number of occasions now, ignored this warning and left it another week or so before getting in the car and driving it off quite normally. So now I don't know whether the Genie is misunderstanding the hybrid system and the role of the 12v Battery and is a bit hypersensitive about it, or whether actually I should be charging the Battery up far more than I am, and that I'm risking not being able to "start" the car...!?  I read, on here, I think, that the cars don't have starter motors as such and the 12v has no possible way of providing the power required to start the engine - which begs the questions: is it true that there is no "starter motor" as such, does the 12v Battery not matter much then if the charge is low, and is my Genie misunderstanding a hybrid 12v battery's role?  Can anyone with hybrid knowledge explain, please?  The answers could all be connected to your issue, I think....

Cheers

[Britprius]

In theory the 12 volt Battery needing to be charged will use more fuel since all the energy for a hybrid car comes from the fuel. However mathematically the amount of energy required to charge the 12 volt Battery in the overall picture is minuscule.
If a 1000 watts of energy (1kw) was put into the 12 volt Battery it would melt. In contrast the electric drive motor in the GS450H is rated at 150,000 watts. The maximum charge rate according to Lexus own figures for the 12 volt Battery is 5 amps. This at 12 volts would be a grand total of 60 watts, and the wind blowing in the wrong direction would have a greater effect.

John 

[Britprius]

1 minute ago, Steve Oliver said:

I have to say the system intrigues me. I have a 2019 NX 300h - and I have an AA Car Genie fitted, which under normal circumstances monitors the car for faults - and on my previous car, a diesel Nissan X-Trail, it would happily tell me that my 12v battery had good charge for weeks on end. Now that the Genie is in my NX, it regularly a day or so after using the car, tells me that the 12v battery is low on charge and could do with a drive to charge it up. I have on a number of occasions now, ignored this warning and left it another week or so before getting in the car and driving it off quite normally. So now I don't know whether the Genie is misunderstanding the hybrid system and the role of the 12v battery and is a bit hypersensitive about it, or whether actually I should be charging the battery up far more than I am, and that I'm risking not being able to "start" the car...!?  I read, on here, I think, that the cars don't have starter motors as such and the 12v has no possible way of providing the power required to start the engine - which begs the questions: is it true that there is no "starter motor" as such, does the 12v battery not matter much then if the charge is low, and is my Genie misunderstanding a hybrid 12v battery's role?  Can anyone with hybrid knowledge explain, please?  The answers could all be connected to your issue, I think....

Cheers

The 12 volt Battery is there to power the accessories, and boot the computers to enable the starting procedure. Part of this procedure after system checks have been done is to pull in relays *electrically operated switches" to connect the traction HV Battery. It is this Battery that starts the engine using one of the two electric motors in the transmission.
If the 12 volt Battery is low the voltages from sensors in the systems are also low or missing preventing the car from going to ready mode, and starting.

John.

[LexIS200Sport]

John, just wondering - is it not the case that the combustion engine fires-up if the 12V Battery so much as needs a top-up? I too noticed that the consumption on the GS450h improved by 2mpg average after a fresh 12V Battery, and that the car switches to EV mode more readily.

With the old 12V Battery, there has been instances where the engine keeps running when the gear lever is in "P" even though the hybrid Battery is at 3 bars+ and the engine has fully warmed up. So although charging the 12V only consumes 60W, the fact that an entire engine is being turned over to provide for this affects the overall fuel economy?

Of course, just from my observation and that I may have read this from somewhere - I may be totally wrong.

 

[Farqui]

David, might the change in economy that you are noticing be due to the on-board computer being reset from the disconnected Battery?

Previously I expect you were seeing accumulated average mpg over many miles/days.

Although when the Battery is disconnected the ECU goes through a relearn process, so maybe you are actually seeing an improvement.

With my inconclusive and contradictory reply, I'll duck out and go for a lie down!

[Herbie]

Toyota/Lexus seem to have skimped a bit in the provision of the 12V Battery. My 'normal' cars have had batteries of 75Ah rating but my RX450h Battery is, if I remember correctly, about 50Ah or even less.

Because a hybrid doesn't have a traditional starter motor it doesn't require such a big, beefy Battery as a normal car. A traditional starter motor draws upwards of 300A to crank the engine, whereas my RX only draws 15.32A to get the car to the READY state, so in that case the smaller capacity Battery doesn't matter.

However, there is always a quiescent current draw for things like the alarm, radio presets and other stuff that needs to be powered up, even when the car is parked up and not being used, which is where the lower Battery capacity makes itself known, in not lasting as long as a higher capacity one.

It also has to be said that traction Battery voltage is not the only cause of the petrol engine firing up. The engine provides heat for the cabin so it will fire up to provide whatever temperature you've got the system set to and to keep it there.

[LordByronUK]

2 hours ago, Farqui said:

David, might the change in economy that you are noticing be due to the on-board computer being reset from the disconnected battery?

Previously I expect you were seeing accumulated average mpg over many miles/days.

Although when the battery is disconnected the ECU goes through a relearn process, so maybe you are actually seeing an improvement.

With my inconclusive and contradictory reply, I'll duck out and go for a lie down!

This was the average mpg just from the trip, not the average since filling up the tank. The average since refill obviously stayed more or less the same with just a slight increase from the last trip of 47mpg.

[jumbojake]

it does make sense, if 12v Battery is low, the engine will fire up to charge that, even if it isn't needed for anything else. 

My worry is I've heard a few people say about this and the lack of notice you get of pending failure.  With a traditional car you get signs of Battery decay when it doesn't start as well.. but with these you have no clue until it doesn't fire the computer.. needs a warning message ahead of the problem!

[Britprius]

4 hours ago, Herbie said:

Toyota/Lexus seem to have skimped a bit in the provision of the 12V battery. My 'normal' cars have had batteries of 75Ah rating but my RX450h battery is, if I remember correctly, about 50Ah or even less.

Because a hybrid doesn't have a traditional starter motor it doesn't require such a big, beefy battery as a normal car. A traditional starter motor draws upwards of 300A to crank the engine, whereas my RX only draws 15.32A to get the car to the READY state, so in that case the smaller capacity battery doesn't matter.

However, there is always a quiescent current draw for things like the alarm, radio presets and other stuff that needs to be powered up, even when the car is parked up and not being used, which is where the lower battery capacity makes itself known, in not lasting as long as a higher capacity one.

It also has to be said that traction battery voltage is not the only cause of the petrol engine firing up. The engine provides heat for the cabin so it will fire up to provide whatever temperature you've got the system set to and to keep it there.

I agree totally, and is why I fitted a 110 AH Battery in my GS last summer. Many on LOC said basically they did not see the point of this, but perhaps surprisingly it cost substantially less than the OEM size Battery.
I am now in a position that the Battery would hold enough charge to keep healthy for the next three months. Of course I am keeping it on charge, but in my situation this is very easy. For others it will not be so possibly requiring the removal of the Battery from the car to take indoors for charging.
I do appreciate that not all cars have the space for a larger capacity Battery, but would urge people to check for this. It may be there is a taller higher AH Battery that would fit in some vehicles where the Battery tray is full with no space around it.

John.

[bluenose1940]

Can someone enlighten me please as to what action. if any, is needed to ensure that my batteries remain in reasonable condition whilst my car is parked up, perhaps possibly for many weeks to come.  At the moment it is just over two weeks since it was last used.

Is there some way that I can check to see what sort of state they are in at the moment?  I have a multimeter but I am not a competent user of it.  can I put it across the 12v terminals to check and if so, what settings will I need to use?

I'm not sure where the 12v Battery is located in my NX, I will have to dig out the manual today and have a look.  If the Battery needs charging, can I do it in situ, or do I need to disconnect the lead to be on the safe side?

If I can get the 12v one healthy, what can I do about the hybrid Battery.  Would it simply be a case of sitting in the car with the engine running for say half an hour?

Thanks for any help that may be offered.

Hope you are all managing to keep safe and well in these difficult times.  Fantastic response to the 8pm applause session last night, can become quite emotional really.  Well done to each and every one of them.

[NemesisUK]

The traction Battery will be fine for many weeks.

The 12v Battery could be hooked up to a maintenance charger, if you have access to mains supply? I have used and would recommend the CTEK mxs 5. Just connect to the 12v Battery and leave connected for the duration. 

[JeffL]

+1. Loads of stuff on here about the CTEK MSX5, just bought one this week. Do a search on LOC for CTEK MSX5

[Steve Oliver]

23 hours ago, Britprius said:

The 12 volt battery is there to power the accessories, and boot the computers to enable the starting procedure. Part of this procedure after system checks have been done is to pull in relays *electrically operated switches" to connect the traction HV battery. It is this battery that starts the engine using one of the two electric motors in the transmission.
If the 12 volt battery is low the voltages from sensors in the systems are also low or missing preventing the car from going to ready mode, and starting.

John.

Thanks John, so one of the electric motors is the starter motor! How come it doesn't need such high current as a normal starter motor?! 🤔 

[jumbojake]

It takes the same 'power' to crank the engine.... as Power = Amps x Voltage ... because  the traction Battery is high voltage, the current drawn is much lower

[Herbie]

1 hour ago, Steve Oliver said:

Thanks John, so one of the electric motors is the starter motor! How come it doesn't need such high current as a normal starter motor?! 🤔 

 

53 minutes ago, jumbojake said:

It takes the same 'power' to crank the engine.... as Power = Amps x Voltage ... because  the traction battery is high voltage, the current drawn is much lower

That may well be the case if we were talking purely about an electric motor but I don't think we are because it's not as simple as energising the motor which then cranks the engine.

Toyota have been extremely clever in developing what they call the Power Split Device or PSD and starting the engine is part of it's duties.

There used to be a great animation here http://eahart.com/prius/psd/ but it seems to have disappeared, although a great explanation of the PSD and the role it plays can still be found at that link.

[Herbie]

It appears that the animation is still there but it needs Adobe Flash to be enabled to see it and interact with it, but it's definitely still there as you'll see below:

[Britprius]

6 hours ago, Steve Oliver said:

Thanks John, so one of the electric motors is the starter motor! How come it doesn't need such high current as a normal starter motor?! 🤔 

As member John "jumbojake" has already replied it is the way power is used in watts. At 12 volts the normal starter might take 250 amps to turn the engine, or 12 X 250 = 3000 watts. The HV Battery is rated at 288 volts so at that voltage the current needed would be 3000 divided by 288 = 10.4 amps. At this current there is also less losses through heat.

The same principle is applied to bring electricity to your home. The overhead grid carries voltages of over 164,000 volts at relatively low current, but when stepped down to 220/230 volts for your home uses higher current. At the high voltage used on the grid there are less losses due to heat, and much thinner cables can be used.

John.

[Herbie]

2 hours ago, Don C said:

The power split device has nothing to do with starting the car.  Motor Generator 1 does it. 

Fair enough, thanks - every day's a school day

[Britprius]

6 hours ago, Don C said:

The power split device has nothing to do with starting the car.  Motor Generator 1 does it. 

I beg to differ.
MG1 drives the sun gear of the power split devise "PSD". This in turn turns the planet gears "all part of the PSD"
If the ring gear "part of PSD" around the planet gears can turn freely the engine cannot start because there is not turning moment of the planet gear carrier to which the engine is coupled "again part of the PSD"
If the car is in park The ring gear is locked from turning by the parking pawl. This now gives turning moment the the planet gear carrier to turn the engine if MG1 is energised.
If the car is in "D", and moving in electric mode powered from MG2 locking MG1 starts the car from the wheels via the ring gear, and MG2 as these are directly coupled to the wheels. So at all times the PSD gears are in use.
In neutral Both MG's are electrically isolated, and free to rotate so the engine cannot be started.

John. 

[bluenose1940]

Thank you chaps for the pointers towards the CTEK MXS 5.0, I will probably invest in one of these but, having searched around, I'm surprised at the price variations on it.  Where is the safest place to buy one from?  I usually buy a lot of stuff from amazon which up to now has always been trouble free.

I have had a look at the manual and it would appear that the 12v Battery is located in the same position as it is in the IS300h and so is easily accessible. With regards to charging, the manual states quite clearly on page 532 "If recharging with the 12v Battery installed on the vehicle, be sure to disconnect the ground cable" this appears contrary to what is being said in this thread.

I mentioned in my original post that I do have a multimeter and could do an initial check of the health of my Battery.  Can someone tell me what setting to use on the meter and, what reading I should get for the Battery for it  to be in good condition regarding the current charge level.

There have been some interesting posts on this thread regarding the technicalties of Battery power etc, pretty much all of which has gone flying over the top of this near 80 year old head!!

Thanks again for all the help chaps, as always, very much appreciated.

 

[Herbie]

Geoff, if you put the meter on the 20V DC* range and put the probes across the Battery while the car is just standing there, you should get a voltage reading that you can compare to this chart:

If you then put the car into the READY mode and test again you should see about 14.5V, which shows that the charging system is working as it should.

I'm not trying to come over as a 'know-it-all' because obviously, I don't, but as I've said in other topics I'm a time-served electrician by trade. When the factory closed down I became a telephone engineer on BT, and after a back injury LED to medical retirement I'm now self-employed doing computer repairs. I'm also a licenced radio ham and dabble in electronics as a hobby.

I mention that, not to blow my own trumpet, but just to explain that I've been in and around the electrical/electronics fields for more than 40 years, and in my honest and humble opinion I cannot find any reason as to why the manual would say that the negative (earth) cable should be disconnected from the Battery unless someone was attempting to use an old-style charger that their dad used to use 30 or 40 years ago.

Modern 'intelligent' chargers have all sorts of magical wizardry to monitor voltage and current levels, and safety circuitry too that monitor temperature, charge rate and other parameters. I can't see any reason at all to disconnect the negative cable when using something like the ctek or a Noco. Having said that, I can't be held responsible if something did go awry 

*If the meter doesn't actually state AC or DC but uses symbols instead, AC is denoted by a wavy line and DC is a solid horizontal line with a dotted line underneath it.

[RgrWynne]

2 hours ago, bluenose1940 said:

Thank you chaps for the pointers towards the CTEK MXS 5.0, I will probably invest in one of these but, having searched around, I'm surprised at the price variations on it.  Where is the safest place to buy one from?  I usually buy a lot of stuff from Amazon which up to now has always been trouble free.

I have had a look at the manual and it would appear that the 12v battery is located in the same position as it is in the IS300h and so is easily accessible. With regards to charging, the manual states quite clearly on page 532 "If recharging with the 12v battery installed on the vehicle, be sure to disconnect the ground cable" this appears contrary to what is being said in this thread.

I mentioned in my original post that I do have a multimeter and could do an initial check of the health of my battery.  Can someone tell me what setting to use on the meter and, what reading I should get for the battery for it  to be in good condition regarding the current charge level.

There have been some interesting posts on this thread regarding the technicalties of battery power etc, pretty much all of which has gone flying over the top of this near 80 year old head!!

Thanks again for all the help chaps, as always, very much appreciated.

 

Geoff got mine from amazon, but have Prime so free delivery 😜 no problems

[bluenose1940]

Thank you herbs, I will give it a go tomorrow morning and will report back.

 

[bluenose1940]

10.55am 06/04/20  I have just checked my Battery and it is showing as 11.51, this appears to be about 15%or so according to Herbies chart.  Time to get a charger methinks.  I do have what I would call a normal charger but I think that I prefer to go to one of the 'smart' jobbies.

With the CTEK MXS 5.0, is it possible to permanently connect this to the Battery and leave the actual charger hanging somewhere safely in the boot so that when charging becomes necessary you can simply plug the mains lead into it?

A further thought, is it possible to check the state of the 12v Battery by putting a mulitmeter across the special jump lead connectors under the bonnet?  Also, would it be possible to connect the smart charger to these terminals and leave it permanently connected under the bonnet.  This would make life even easier to connect the mains cable as my car is always parked nose first in front of the garage (nay workshop) door and would avoid the need to mess around in the boot area, or are these connectors equally fiddly to get at.