12v Battery, the Achilles heel

[Boosh.]

Hi, I have no idea if any Lexus owners have experimented with this, but, on recent Toyota hybrid cars, where 'keyless entry' is featured, that option can be turned off via a dashboard menu or even Techstream. 

I have an idea that after approximately a week of complete inactivity, some models will actually do something similar to automatically save Battery power.

From measurements I've seen, the quiescent loading on the Battery is reduced from about 50mA to about 30mA when this keyless entry function is disabled. 

But, in doing this, the keyless 'Start' button function is also disabled, so the ignition key fob has to be held against the 'stop/start' button for the key to be recognised when the button is pressed, and this is not always instant as it usually is - several attempts are often needed.  

The keyfob door lock 'open/close' buttons work as before with this keyless option set to off.  I have no idea what this option is called on Lexus dash menus or Techstream.  On a Toyota I think it might be labelled as 'Auto entry cancel SW', or similar, at least it is when viewed through the Techstream configuration menu.

Perhaps this information is of some use to eke out your 12v Battery charge when your car is not being used?

[Herbie]

2 hours ago, ColinBarber said:

Possibly not the best example as servicing of the aircon system isn't deemed an owner's task and therefore wouldn't be in the owners manual. In fact doing it incorrectly in the UK could mean you are breaking the law. For the competent person, they would know to look in the engine bay where there is an information sticker stating ND11 is required on Lexus hybrid vehicles.

Yeah, sorry, bad example, although someone must buy those 'off the shelf' cans of refrigerant from places like Halfords. Personally I'd take it to a proper aircon specialist.

[Herbie]

31 minutes ago, Boosh. said:

Perhaps this information is of some use to eke out your 12v battery charge when your car is not being used?

Good post Mike but I think it's only for the later versions. I know that for the RX at least, it's only applicable to the series 4, from 2015 onwards.

Some models can even do it by pushing and holding the lock and unlock buttons on the key fob for a couple of seconds, or something like that. It doesn't apply to mine so I didn't pay too much attention to it.

[Brechin Slate]

9 minutes ago, Herbie said:

Good post Mike but I think it's only for the later versions. I know that for the RX at least, it's only applicable to the series 4, from 2015 onwards.

Some models can even do it by pushing and holding the lock and unlock buttons on the key fob for a couple of seconds, or something like that. It doesn't apply to mine so I didn't pay too much attention to it.

Like this?

[Boosh.]

Yes, that's it. The top  part of the page is what I was mentioning, but on some Toyotas, you can configure the car so that it defaults to that 'lower power' mode immediately, rather than having to wait for the car to do it after some (albeit quite small) Battery discharge has taken place.

Also, it's a small potential saving, but every time you walk closely past your car with your 'Keyless entry' keys in your pocket, the car's computers 'wake up' (in anticipation of you getting in, I'd guess) and the interior lights turn on.  It can be another 20 minutes before all the computers go back to 'sleep' and into the previous 50mA drain mode.  For some people this could be an easily avoidable Battery drain. 

On the lower part of that page, as you almost certainly know, that mode is for saving the CR2032 button call (or whatever) in your key fob, and this helps prevent your car from being 'key-cloned' if you are not already storing your keys in some sort of Faraday cage when parked, of course, and it will stop the 12v Battery drain that I've mentioned happening in my paragraph 2, when the key fob is in that mode.

'Teacher', 'eggs' and 'suck' is springing to mind in this answer!  Hopefully, not all of it.

[Mincey]

Permission to digress slightly. It isn't only Lexuses which suffer from this. Some years ago, a chum bought a TVR Chimera (I think it was a Chimera - it's not really important if it wasn't one of those) which had a feature whereby when the door was opened, the window dropped slightly for some reason which I can't remember. Anyway, he had a party soon after purchasing said car and all his friends thought that his new steed's party trick was rather incredible (this was about 1999) and many spent the night playing "let's open the car door again. And again". He wasn't quite so chuffed the following morning when, after recovering from his hangover, he decided to go for a thrash. You guessed it - flat Battery.

[ColinBarber]

13 hours ago, Herbie said:

Some models can even do it by pushing and holding the lock and unlock buttons on the key fob for a couple of seconds, or something like that. It doesn't apply to mine so I didn't pay too much attention to it.

That only saves the Battery in your key fob not the vehicle's Battery.

You need to turn off the smart door locking within the menu of the vehicle to disable the feature which will stop the vehicle sending out signals to try and find a nearby key.

[Thackeray]

13 hours ago, Boosh. said:

Hi, I have no idea if any Lexus owners have experimented with this, but, on recent Toyota hybrid cars, where 'keyless entry' is featured, that option can be turned off via a dashboard menu or even Techstream. 

I turned mine off four or five months ago in the hope that it might reduce Battery drain. I can't remember the exact menu steps but the manual says it's Menu/Setup/Vehicle.

However, I'm not sure that it's had much of an impact. The Battery still needs to be charged every week. I haven't tried turning it on again to compare and I don't know where I could measure the Battery drain with a multimeter. If it's easy to do, maybe someone can tell me how to do this. But the thing is, I suspect that as soon as you open the car all the electronics wake up so it would be hard to measure the Battery drain in its sleeping state.

When I left a Carista OBD adapter plugged in for a week that had a much bigger impact and pushed the voltage down to around 11.5 volts.

[Brechin Slate]

11 minutes ago, Thackeray said:

When I left a Carista OBD adapter plugged in for a week that had a much bigger impact and pushed the voltage down to around 11.5 volts.

Prizmos say that the Carista drain is negligible but experience has shown me otherwise!

 

A: The power drain is relatively low, roughly equivalent to an active GPS alarm system. So unless you leave your car undriven for extended periods of time or you have Battery issues, the power drain aspect should be fine. However, we still do not recommend leaving the device plugged in because it leaves a Bluetooth connection to your OBD port active at all times... and while we're not aware of any exploits of this, it's just safer to unplug it when you're not using it. see less

Prizmos Ltd.

 · 3 years ago

[Mincey]

That's three of us who have experienced Carista generated drain then.

[Boosh.]

1 hour ago, Thackeray said:

I don't know where I could measure the battery drain with a multimeter.

Exactly, measuring the current drain is painfully involved.  But, the figures I've mentioned have been taken with a DC current clamp meter, so very straightforward and no dismantling of wiring needed at all

These meters used to be expensive, but a model came out a few years back at a fraction of the price (although it's gone up £10 in the last month, I wonder why?) - a UNI-T 210E.

The build is only ok, and the ergonomics are only ok, too (it's a bit too slender and small, but then it has to be for its role), but the DC current clamp is great!  It was £30 a few years back, but it's around £50 now, I notice.  It's sensitivity means that it needs careful re-zeroing (a button press) in use, but that's inevitable given the physics of the device!

You can just place this over the Battery earth lead (it has to be a single conductor that is being measured), or the large Battery feed into the fuse box, or anywhere else convenient. 

AC current meters have been cheaply available for ages - it's the DC range that sets this model apart.

I have no links with the company or its sellers - I just like seeing how things work!

[Brechin Slate]

3 hours ago, Mincey said:

the window dropped slightly for some reason which I can't remember.

My Mini Cooper S had this too, I thought it was to protect your eardrums from the pressure increase when you slammed the door whilst inside the car (some people do).  It's more to do with the sealing of the frameless glass at the top of the door seal without stressing either. Another thing to go wrong, I had endless electrical problems with that car from day 1 (indicators didn't work) and it was brand new.

[Maxz]

For anyone interested in saving a few mA by switching off the smart entry (and/or for security reasons). Menus shown for a 2015 standard nav system I believe.

 

[Herbie]

12 hours ago, Boosh. said:

You can just place this over the battery earth lead (it has to be a single conductor that is being measured),

Usually that's correct but not in this case. My Battery negative has two or three leads coming off it so to measure the total quiescent current I would need to clamp round all of them. Of course, it's just semantics really because it could be one big thick one or it could be three smaller ones, it doesn't matter - all are connected to the same negative Battery post.

[200h]

19 hours ago, Brechin Slate said:

My Mini Cooper S had this too...............and from day 1 (indicators didn't work) and it was brand new.

standard feature from the Bmw stable ( wasnt ticked on the options list)

[Mincey]

2 hours ago, 200h said:

standard feature from the Bmw stable ( wasnt ticked on the options list)

Or the blinker fluid is low or has run out:
 

 

[Paul Brooksbank]

Would an 8 AA cell holder be enough to get the computer booted up?

 

[Herbie]

32 minutes ago, Paul Brooksbank said:

Would an 8 AA cell holder be enough to get the computer booted up?

In theory, yes it would.

It's been a long time since I looked for the data but if I remember correctly, the discharge curves say that it would produce about 20A, rapidly falling to full discharge in less than a minute.

I won't be upset if anyone proves me wrong because as I said, it's been a long time and I can't be bothered hunting it all out again. What I can say, with confidence, is that my 2013 RX450h takes less than 20A (possibly even less than 15A) to achieve READY mode.

[Boosh.]

I'd thought about doing this a while back. I'm certainly no expert here, and I'm happy to be corrected if my following thoughts are way off!  But we're in lockdown, so this 'thought-roaming' allows a useful distraction.  So, off the top of my head:-

An alkaline AA cell has a large internal resistance that stops it producing high currents, but the arrangement above could be used if it were just attempting to slowly 'top-up' the existing 12v Battery to get it to a working state.  I think an AA alkaline cell would provide roughly 2500 mA if it was discharged slowly. 

A NiMH AA cell could produce produce 7 - 10 Amps for a short while as it has a much lower internal resistance, but it would get quite hot while it was doing it and so be less efficient in that usage pattern, with an optimum capacity of 2500mAh again.  With the NiMH, you'd also need a 10-battery holder to accommodate for the reduced voltage (1.2v) vs an alkaline cell, no? 

Even at the AA cell's maximum current output, I think you'd still have to anticipate just using them to recharge the existing 12v Battery, as the normal start currents required would be way above what they could otherwise support, e.g. not least because the brake booster motor, when it automatically starts, could well pull quite a hefty current for around 5 seconds, especially initially.

The Battery holder shown might 'wilt' doing this sort of work, as it's normally used in much lighter duty applications, and the connectors and wires wouldn't be rated for this.  Or, looking at it another way, if they were up for this, why were they so generously specified by the Chinese manufacturer?

I would really like this to work.  If you wanted to experiment (which i might yet do myself), then I'd suggest putting a conventional car headlamp bulb in series with a feed wire, to offer some current limiting if it all goes a bit mad!  And you have to make sure none of the cells got too hot else there is a serious explosion risk.

If this did all work as best it could, then you're still only going to get about 2 Ah of charge into your 12v Battery, is that enough? 

FWIW, I think inside these small booster/starter packs that are common nowadays, is simply a small group of 18650 Lithium cells (google it!) which have become the industry standard in the rechargeable Li Battery world, a bit like the AA cell has become - which it actually looks like a scaled-up version off.  

For a quick example, early Teslas, some (all?) electric bicycles, vaping devices, and even my cheap, recently-bought Screwfix worklight, all take different numbers of an 18650 cell of basically the same physical size, voltage and chemistry.  But their internal resistance is really low - as the Tesla's acceleration reveals.

Realistically, It's not going to work unless the 12v Battery was almost charged enough beforehand, but I'd be fun seeing why it didn't work in practice.

[Herbie]

1 hour ago, Boosh. said:

Even at the AA cell's maximum current output, I think you'd still have to anticipate just using them to recharge the existing 12v battery, as the normal start currents required would be way above what they could otherwise support, e.g. not least because the brake booster motor, when it automatically starts, could well pull quite a hefty current for around 5 seconds, especially initially.

I've never actually tried the 8 AA cells so I don't know if it would work in reality or not.

However, 5 seconds is far too long. From pressing the Power button to getting the green READY light on the dash takes approximately two seconds - counting one-one thousand, two-one thousand, I don't even get to start saying three-one thousand before it lights up.

This is what makes me think that it would actually work. Eight cells providing 2500mA = 20A, but it's only needed for about 2 seconds. Unless they just explode almost immediately they should be capable of doing it...I think

Below are two photos I took a while ago. Not very scientific but gives an insight. I apologise that one of my rapidly diminishing hairs seems to have escaped from my scalp!

The first one shows that with the doors open, internal courtesy lights on, radio on and maybe something else, I can't remember, the car is drawing 2.63A.

I then got my wife to sit in the driver's seat, put her foot on the brake pedal and press the power button. The current draw shot up but it was too fast to see. I can say that to the best of my knowledge it didn't go above 20A because I don't remember seeing anything above a 2 as the first digit, but it happened so fast that I didn't even have time to press the yellow 'HOLD' button on the meter to grab the highest reading before the current flow changed polarity (shown by that black line under the 'DC') and the DC/DC converter started squirting 9.6A from the car back into the Battery.

[ColinBarber]

15 hours ago, Herbie said:

However, 5 seconds is far too long. From pressing the Power button to getting the green READY light on the dash takes approximately two seconds - counting one-one thousand, two-one thousand, I don't even get to start saying three-one thousand before it lights up.

This is what makes me think that it would actually work. Eight cells providing 2500mA = 20A, but it's only needed for about 2 seconds. Unless they just explode almost immediately they should be capable of doing it...I think

It will be more that 5 seconds. As soon as you connect the Battery pack to the vehicle's 12v system it will be charging the vehicle's flat 12v Battery and will very quickly pull down the voltage of AA batteries. By the time you have connected it up and turned on the ignition you may be too late.

 

AA batteries aren't 2500mA, they have a capacity of 2500mAh. Manufactures don't normally specify the Amps they can provide but internal resistance of non-rechargeable batteries will limit it to just a few Amps.

Eight cells connected to provide 12v are connected in series. Current is a constant through a series circuit. If one Battery could provide 2.5A the whole Battery will provide 2.5A, not 20A.

[Herbie]

14 hours ago, ColinBarber said:

Eight cells connected to provide 12v are connected in series. Current is a constant through a series circuit. If one battery could provide 2.5A the whole battery will provide 2.5A, not 20A.

Of course, you are correct - I made a right schoolboy error there didn't I  That's what happens when you try to rush out answers between doing other things. I'm off to bed, tomorrow can only be better

[Colin Crow]

On 1/20/2021 at 11:52 PM, Maxz said:

For anyone interested in saving a few mA by switching off the smart entry (and/or for security reasons). Menus shown for a 2015 standard nav system I believe.

 

Thanks for this, Maxz. I've just followed the steps and I'm hoping that this will extend the amount of time the Battery remains charged while not in use. I would add that the Power button needs to be pressed twice before the Car Customisation options are available (on one press they are greyed out) - not sure why this surprised me, but it did. Incidentally, I couldn't find this information in the User Guide but maybe I just missed it.

[S.H.]

hi guys.. I bought a Lexus IS 300H F-Sport 2017" with just 10.000km on it few months ago and when I did ask for service history from the Lexus dealer he told me that the car just got a new 12v Battery, so this can be a problem. I am an old mechanic so after some reading then the problem is easy to see... we the customers want all the luxury in the world and that means anti theft systems, automatic lights, folding mirrors, keyless entry that is always in ready mode and in my car moving seats and moving steering wheel. All before the car has been started.. then we can see there is a drain on the 12v Battery no matter what type of car it is and it is just a matter of how much not if, then comes the last variable and that is cold or warm climate....  yes and how good the Battery is cos it is not new (except mine ) so the only question is how to prevent it from getting dead.. I am using c-tek to top up when needed but have not yet done it properly the connection (I just clamp on the terminals the old style) I know in USA they use a magnetic system (I found this on a Corvette site and as we all know they are not hybrids..) as a plug that is connected to the Battery terminals with a fuse in the line and the magnet is mounted under the rear bumper or in the front grill. So the only thing needed when you park your car for extended time is to put the magnet that is mounted to the charger to the magnet on the car and plug the charger to the grid. This is the most simple solution that I have seen so far.... and on the plus side is if we forget to unplug the magnet when we go then the only thing that happens is the magnet just bounces off and no damage. In BMW they just say unplug the Battery if more than a week. For the airport I would probably use a small extra Battery but the best solution would be 12v to 12v charger, that is no doubt the healthy way to charge a dead Battery when off grid.   kind regards.

Page 633 ■ To prevent 12-volt Battery discharge ● Turn off the headlights and the audio system while the hybrid system is off. ● Turn off any unnecessary electrical components when the vehicle is running at a low speed for an extended period, such as in heavy traffic.

■ Charging the 12-volt Battery The electricity stored in the 12-volt Battery will discharge gradually even when the vehicle is not in use, due to natural discharge and the draining effects of certain electrical appliances. If the vehicle is left for a long time, the 12-volt Battery may discharge, and the hybrid system may be unable to start. (The 12-volt Battery recharges automatically while the hybrid system is operating.) ■

[mujib1]

On 1/17/2021 at 4:29 PM, Brechin Slate said:

Here you go Alan, made this earlier, hope it helps:

https://youtu.be/7K4HELfg3hw

Hi

Thanks for posting that video very useful.

 

Would like some clarification if anyone can help advise please. i have a flat Battery, no electrics etc. I am thinking about getting a NOCO GENIUS5UK Smart Battery Charger. Cannot leave it charging overnight as car on road outside home. Will this devise be OK to in effect charge for a short while to get car started so I can keep running for 60 mins etc?

 

Also, does this(NOCO charger terminals) connect to Battery in boot on IS300H and not under the hood? Would jump starting my car using another car need connecting under the hood (that's what it says in my manual). Just a bit confused about the terminals between hood and boot where I see the 12V Battery.

 

Many thanks in advance!