nx 300h 12 volt battery

[Medora]

Hi All,

     My 12 volt Battery ( starter etc ) only holds its Charge for two/ three weeks if I don’t drive the car. Once it’s flat it’s really flat!

Any  one else had this issue ? 

[JHRyan]

Yes - first week in March my car - NX 450+ (2022) wouldn't start up - i had to get Lexus Assist - it appears that it was the 12v Battery - i charge the car about twice per week - so i was surprised to find that the 12v Battery was empty!

[HMT]

48 minutes ago, Medora said:

Hi All,

     My 12 volt battery ( starter etc ) only holds its Charge for two/ three weeks if I don’t drive the car. Once it’s flat it’s really flat!

Any  one else had this issue ? 

Yes had this on my 15 plate 300h a couple of years ago. Called out RAC they checked and said 1 of the cells had gone and should think about replacement.  Had it in for service at Lexus a couple of weeks later and had pre warned them I would need the Battery replaced.

on collection was told Battery ok and that RAC “did not know how to check these batteries” 

About 3 weeks later got a flat Battery and had to call out RAC - they do not like repeat callout to same fault.  The inspected Battery - now 2 cells gone.  
got them to replace (not cheap) and has been fine since

suggest you go to a local dealer and get the Battery checked

[NiCoRe]

Charging the traction Battery does not charge your 12V Battery.
And as illogical as it seems at first, 12v Battery may be drained when you leave the car plugged because, it is used to keep the charging controllers "awake" through the process and will keep them "on" as long as the car is plugged (even when charging is over). 12 v Battery is used to start the accessories of the car and make it ready to start rolling.

It gets recharged when you drive the car long enough :

• in EV mode by draining a tiny part of electricity from the traction Battery
• in HV mode when the ICE is on

It charges very slowly in order to get the longest Battery life possible (as in any car) 

YouTube LFST made a pretty interesting video when his 12V Battery died 

https://youtu.be/7OtsgIpe3CQ

[NiCoRe]

1 hour ago, Medora said:

Hi All,

     My 12 volt battery ( starter etc ) only holds its Charge for two/ three weeks if I don’t drive the car. Once it’s flat it’s really flat!

Any  one else had this issue ? 

If it is still the original one, it is over 7 years old...
Nothing abnormal considering the small size of 12v batteries on hybrids to have it replaced by a new one.
You can also use a trickle charge system (if you have one) to try to extend its lifespan

[NiCoRe]

34 minutes ago, HMT said:

Yes had this on my 15 plate 300h a couple of years ago. Called out RAC they checked and said 1 of the cells had gone and should think about replacement.  Had it in for service at Lexus a couple of weeks later and had pre warned them I would need the battery replaced.

on collection was told battery ok and that RAC “did not know how to check these batteries” 

About 3 weeks later got a flat battery and had to call out RAC - they do not like repeat callout to same fault.  The inspected battery - now 2 cells gone.  
got them to replace (not cheap) and has been fine since

suggest you go to a local dealer and get the battery checked

RAC or any "side of the road" assistance service will never check a traction Battery health (the high voltage one which is used by EV mode).
They can and will check the 12 v Battery.
You need special equipment to check the traction one and that is what the dealership does during scheduled maintenance. 

[HMT]

24 minutes ago, NiCoRe said:

RAC or any "side of the road" assistance service will never check a traction battery health (the high voltage one which is used by EV mode).
They can and will check the 12 v battery.
You need special equipment to check the traction one and that is what the dealership does during scheduled maintenance. 

Yes we are talking about the 12v Battery - not the traction Battery.

the original post clearly states this, and I was referring to the RAC checking the 12v only and the Lexus dealership checking the 12v - the normal Hybrid (traction battery) was a seperate check

[NiCoRe]

Well, "pardon my French", if may say so ! 😇

"on collection was told Battery ok and that RAC “did not know how to check these batteries "'

I read your post probably too fast and understood that your Lexus dealer gave you the feedback on your traction Battery only as no one can reasonably states that RAC doest not know how to check 12V batteries.

[HMT]

4 minutes ago, NiCoRe said:

Well, "pardon my French", if may say so ! 😇

"on collection was told battery ok and that RAC “did not know how to check these batteries "'

I read your post probably too fast and understood that your Lexus dealer gave you the feedback on your traction battery only as no one can reasonably states that RAC doest not know how to check 12V batteries.

1 of several reasons I no longer use that dealership

[Herbie]

19 hours ago, Medora said:

Hi All,

     My 12 volt battery ( starter etc ) only holds its Charge for two/ three weeks if I don’t drive the car. Once it’s flat it’s really flat!

Any  one else had this issue ? 

You should be getting more than two or three weeks out of it but it sounds like you've let it discharge too far and it's damaged something. Every time it goes flat it causes slight damage that reduces its capacity, by which I mean that if you buy a brand new one and charge it up, the charger will cut out at 100% (fully charged). The more it's allowed to go flat, the sooner the charger will cut out, say at 80%, thinking it's fully charged because it can't shove any more in.

You can make a (very) rough calculation to show how long it should hold charge, but it's really too vague to be of any practical use but...

My RX has a 60Ah Battery in it, which means that it can supply 60A for one hour, or 30A for two hours and so on.

There will always be a quiescent current draw from the Battery to keep certain things 'alive', such as the alarm, the clock, the radio presets and the seat memory, perhaps even more. This current draw is generally accepted to be 50mA or 0.05A.

If we assume a brand new and fully charged Battery, that means  60Ah divided by 0.05A = 1,200 hours to go from fully charged to fully  discharged, which is  50 days or 7.14 weeks.

Remember though, that the Battery will be unable to provide enough power to start the car long before it becomes fully discharged, so you'll never actually get that 7.14 weeks in reality. Not forgetting that every time it goes flat it loses some capacity, which means that it can't hold as much charge as it used to anyway.

There is also a possibility that there's a fault somewhere that's causing a higher current draw and therefore flattening the Battery quicker than it should. This is called a 'parasitic drain' and you really should check to make sure it's not that.

[Medora]

31 minutes ago, Herbie said:

You should be getting more than two or three weeks out of it but it sounds like you've let it discharge too far and it's damaged something. Every time it goes flat it causes slight damage that reduces its capacity, by which I mean that if you buy a brand new one and charge it up, the charger will cut out at 100% (fully charged). The more it's allowed to go flat, the sooner the charger will cut out, say at 80%, thinking it's fully charged because it can't shove any more in.

You can make a (very) rough calculation to show how long it should hold charge, but it's really too vague to be of any practical use but...

My RX has a 60Ah battery in it, which means that it can supply 60A for one hour, or 30A for two hours and so on.

There will always be a quiescent current draw from the battery to keep certain things 'alive', such as the alarm, the clock, the radio presets and the seat memory, perhaps even more. This current draw is generally accepted to be 50mA or 0.05A.

If we assume a brand new and fully charged battery, that means  60Ah divided by 0.05A = 1,200 hours to go from fully charged to fully  discharged, which is  50 days or 7.14 weeks.

Remember though, that the battery will be unable to provide enough power to start the car long before it becomes fully discharged, so you'll never actually get that 7.14 weeks in reality.

 

[Medora]

Hi Herbie,

    Thank you the info, I think you have summed it up perfectly .

Colin