12V battery problem

[Alan Thompson]

1 hour ago, ColinBarber said:

1 - Yes

2 - Don't. To 'jump' the vehicle, connect your battery pack directly to the battery once you open the bonnet.

The Battery is not under the bonnet (it's in the boot). However, the jump start points ARE under the bonnet - see  pages 727 & 728 of the user manual.

[ColinBarber]

29 minutes ago, Alan Thompson said:

The battery is not under the bonnet (it's in the boot). However, the jump start points ARE under the bonnet - see  pages 727 & 728 of the user manual.

Yes of course, apologies.

Using the jump points in the engine bay means you don’t have to get the boot open if the Battery is located there. 

[Harrier Man]

I had my dealer show me exactly where to connect; more memorable and comforting than relying on an illustration on a dark, wet winter's night.

[ColinBarber]

5 minutes ago, Harrier Man said:

more memorable and comforting than relying on an illustration on a dark, wet winter's night.

Yes, certainly worth familiarising yourself in ideal conditions where the jump point is before you actually need it.

[Andy B]

The only slight issue with connecting to Lexus' suggested jump starter terminals under the bonnet (notably point D as referenced in the manual) is that the jump leads provided with most jump starter packs are notoriously short so may not stretch that far.

[Mike100C]

1 minute ago, Andy B said:

The only slight issue with connecting to Lexus' suggested jump starter terminals under the bonnet (notably point D as referenced in the manual) is that the jump leads provided with most jump starter packs are notoriously short so may not stretch that far.

Hi Andy, agree with your observation the suggested earth point on the engine block is way too far for my jump pack. I suggest connecting to a suitable bolt head/thread earth point.

[Harrier Man]

The suggestion from my dealer was to use one of the bolts at the top of the suspension strut for the earth connection. He acknowledged that this wasn't the official point but is 'what they used'. This is a lot closer than Point D but I admit that I haven't tried my NoCo leads to see if they are long enough.

[ColinBarber]

11 hours ago, Andy B said:

The only slight issue with connecting to Lexus' suggested jump starter terminals under the bonnet (notably point D as referenced in the manual) is that the jump leads provided with most jump starter packs are notoriously short so may not stretch that far.

The recommendation seems to be Toyota's standard procedure when the Battery is in the engine bay - ideally you don't want to connect to the -ve on the Battery (which will cause a spark) in case there is hydrogen gas present so they suggest a remote connection. This precaution makes no sense when the Battery is located in the boot and your jump points are in the engine bay.

Any good earth point can be used.

[Solihullman]

I have the same problem with my 2023 450h+. I won't repeat what everyone is saying other than to add that I travelled home from North Wales last Saturday, running entirely on petrol, did  about 50 miles on Sunday and similar on Monday, then this morning - Battery flat. So it is not primarily when a car has not been much used that the 12v Battery dies. This has happened to me twice in the 9 months I have had the car. It completely disables the car which can be a disaster. The boot cannot be opened manually so it can be very difficult to access the Battery - you have yo go in through the back seat, if you can open that door. It seems to me like a 'Don't buy this car' issue.

[Warthog001]

That doesn't seem like the parasitic draw that most of us suffer from - could it be a DC to DC converter issue?

[Alan Thompson]

6 hours ago, Solihullman said:

I have the same problem with my 2023 450h+. I won't repeat what everyone is saying other than to add that I travelled home from North Wales last Saturday, running entirely on petrol, did  about 50 miles on Sunday and similar on Monday, then this morning - battery flat. So it is not primarily when a car has not been much used that the 12v battery dies. This has happened to me twice in the 9 months I have had the car. It completely disables the car which can be a disaster. The boot cannot be opened manually so it can be very difficult to access the battery - you have yo go in through the back seat, if you can open that door. It seems to me like a 'Don't buy this car' issue.

Why do you need to access the Battery when you can still open the bonnet and access the jump start points in there?

[ColinBarber]

6 hours ago, Solihullman said:

I have the same problem with my 2023 450h+. I won't repeat what everyone is saying other than to add that I travelled home from North Wales last Saturday, running entirely on petrol, did  about 50 miles on Sunday and similar on Monday, then this morning - battery flat.

There were issues with the earlier RAV4 PHEVs with one of the systems not shutting down correctly and causes an excessive power drain. It would be worth asking your dealer to check all firmware is up to date. Otherwise there is some other issue - this isn't the normal problem that most hybrid owners suffer from.

[Petersan65]

I am new to this Forum but have been amazed about how many owners 350/450h owners have had problems with the 12 v auxiliary Battery going flat. I thought I was the only one!

I have a 350h+ which was purchased new in Nov 2022 and have had 3 occasions ( 2 within one month) when the Battery went completely flat with the embarrassing lock out from the car. Each time I called the AA who jumped started the car and recommended I took it to the Lexus dealer. Each time the dealer checked the car and Battery and said there were no technical issues. They told me that the Battery is going flat because of low mileage/intermittent usage which seems to be a familiar story with many other users.

Looking through many of your responses I am encouraged that many of you have found a "work around" to the issue by using trickle chargers/booster packs/voltage meters and turning off all electrical systems when leaving the car. 

Whilst I love the car it has become unreliable. Does anybody know if this issue is being worked on by Toyota? Would a larger auxiliary Battery fix the issue?

This is a luxury car (LEXUS=Luxury USA) and we should not have to be using trickle chargers or booster packs!

[NemesisUK]

15 minutes ago, Petersan65 said:

This is a luxury car (LEXUS=Luxury USA) and we should not have to be using trickle chargers or booster packs!

I think you will find many 'luxury' marques have this 'issue'. Mercedes for example supply trickle chargers with their top-end sports cars simply because they know the cars will be driven less frequently.

The fact that not all NX owners suffer this problem leads one to believe it must be a usage or car specific issue, for example, perhaps poorly fitted extras causing a parasitic drain?

 

[stepppy]

Rather than start a new thread, I thought I would tag onto this one.

I am hopefully picking up my new NX350h AWD next week, but I am going on holiday a few weeks after for nearly four weeks.  I am familiar with using a smart charger as I use one on my Prius when I go away and have it linked to a smart plug so it comes on twice a week for 8 hours per day.

My question is, on my Prius it was easy as the Battery is under the bonnet, but the NX is in the boot.  Do I have to connect the charger to the terminals in the boot or can I use the jump points under the bonnet?

Or will I be OK as it will be a new Battery rather than my original 7 year old Battery I currently have?

Thanks.

[ColinBarber]

4 hours ago, stepppy said:

My question is, on my Prius it was easy as the battery is under the bonnet, but the NX is in the boot.  Do I have to connect the charger to the terminals in the boot or can I use the jump points under the bonnet?

Or will I be OK as it will be a new battery rather than my original 7 year old battery I currently have?

I would connect the charger to the terminals in the engine bay as it's easier to pass the cables out through the bonnet/grill than the boot.

Not sure I'd bother with a smart plug, if it's an intelligent charger that backs off when the Battery is fully charged these can be left on indefinitely.

 

I'd imagine that your Battery would be okay if you just left the vehicle but you would be discharging it unnecessarily (and shortening its life) if you have the means to keep it charged up. If you did this then I'd recommend turning off smart entry to help save a bit of power.

[stepppy]

48 minutes ago, ColinBarber said:

I would connect the charger to the terminals in the engine bay as it's easier to pass the cables out through the bonnet/grill than the boot.

Not sure I'd bother with a smart plug, if it's an intelligent charger that backs off when the battery is fully charged these can be left on indefinitely.

 

I'd imagine that your battery would be okay if you just left the vehicle but you would be discharging it unnecessarily (and shortening its life) if you have the means to keep it charged up. If you did this then I'd recommend turning off smart entry to help save a bit of power.

Thanks Colin, that’s good to know. The car will be garaged, so I will connect it to the points under the bonnet. If the negative lead doesn’t reach the place stated in the manual is there an alternative place you would recommend?

[ColinBarber]

33 minutes ago, stepppy said:

The car will be garaged, so I will connect it to the points under the bonnet. If the negative lead doesn’t reach the place stated in the manual is there an alternative place you would recommend?

If in a garage then you potentially could directly connect to the Battery and not fully close the tailgate (turn off the interior boot light).

In the engine bay I believe Lexus suggest the left hand side of the engine - I'd imagine any of the bolts that hold brackets against the metalwork would be just as good as long as you can get a good mechanical connection to your charger lead. I wouldn't use the three bolts from the suspension strut as those will be insulated underneath and may not have a good earth on top because of the paint.

[NemesisUK]

I don't think any of the boot/bonnet/tailgate seals are tight enough to not allow the thin cable form the charger to pass through when fully closed. The seals are quite compliant. I trickle charge my AMG via the closed boot without issue.

[DavidCM]

The boot seal on my RC easily closes on my Noco trickle charger cable,with no damage to either seal or cable.

[Harrier Man]

On 2/29/2024 at 1:57 PM, Harrier Man said:

The suggestion from my dealer was to use one of the bolts at the top of the suspension strut for the earth connection. He acknowledged that this wasn't the official point but is 'what they used'. This is a lot closer than Point D but I admit that I haven't tried my NoCo leads to see if they are long enough.

My NoCo leads are very short and wouldn't reach the official earth point but they do reach the dealer suggested point for a jump start.

For Steppy and others, I wouldn't necessarily use this for a charger and I certainly wouldn't be loosening a suspension nut to create a more permanent connection. I agree with Colin that paint may interfere with a good connection. The dealer did point out another bolt on the bodywork (around the headlight area) that can be used but I wasn't paying close attention to its location and I don't have a photo; however, this could be an alternative, albeit subject to the same caveat about paint.

[Scotlex]

18 hours ago, stepppy said:

Rather than start a new thread, I thought I would tag onto this one.

I am hopefully picking up my new NX350h AWD next week, but I am going on holiday a few weeks after for nearly four weeks.  I am familiar with using a smart charger as I use one on my Prius when I go away and have it linked to a smart plug so it comes on twice a week for 8 hours per day.

My question is, on my Prius it was easy as the battery is under the bonnet, but the NX is in the boot.  Do I have to connect the charger to the terminals in the boot or can I use the jump points under the bonnet?

Or will I be OK as it will be a new battery rather than my original 7 year old battery I currently have?

Thanks.

My NX has been left in the garage for about 3 and a half weeks and "started" all OK yesterday.

Hope this helps.

I would prefer not to use a trickle charger.

[Mike100C]

9 hours ago, DavidCM said:

The boot seal on my RC easily closes on my Noco trickle charger cable,with no damage to either seal or cable.

I use the Noco extension lead on my NX 450h+ and it works fine with boot closed as well. No marking or damage as stated above.

[stepppy]

25 minutes ago, Scotlex said:

My NX has been left in the garage for about 3 and a half weeks and "started" all OK yesterday.

Hope this helps.

I would prefer not to use a trickle charger.

Thank you, that's encouraging to hear.  I guess I am a bit wary of causing damage to the 12v Battery if it was to go flat, not sure how much damage it causes if it was to only happen once.  I have been used to doing it on my Prius due to it being the original Battery and not wanting to have to fork out for a new one before I changed the car 😬

The charger I have is a smart one so is designed to be left on for long periods of time, but I am a bit of a worrier about leaving things on that are not normally, especially this time with the car being brand new.

Thanks to everyone else to their tips and advice, it's very much appreciated 😀

[Simpson Iain]

I have recently acquired a Lexus 2019 NX300h, and after reading posts on this forum on issues with the 12v Battery, have started monitoring Battery voltage with a digital multimeter. I have noticed that the voltage reduces the longer I do not drive the car. The lowest I have measured is 12.1v after not using the car for two days.

Is there a critical voltage below which the car will not go into ready mode?

I have just ordered some electrical components to allow me to easily connect an existing trickle charger to the Battery. I have also ordered a voltmeter that can plug into the OBD2 socket to monitor Battery voltage.