Lexus RC300h standing unused, 12v battery concerns

[mickdupleD]

I have an elderly friend with a Lexus RC300h and he is unable to drive it for six months due to having had a heart operation. He has covered the car up on his driveway. I was concerned that the 12v Battery may discharge over time, due to alarms and immobilizers. I have a 'smart' Battery charger and wanted to loan it to my friend, to periodically top up the 12v Battery. He allowed me to look at his car, but I knew nothing about the RC300h at the time. My own car is a Volvo with a front mounted Battery, and to trickle charge that, I connect the +ve charger clamp to the +ve Battery terminal, and the -ve clamp to an earth point, and it charges fine. This is what I expected to do on the Lexus, but initially I could not find the 12v Battery, and my friend's Lexus handbook was very little help! 

I have since discovered from online sources the 12v Battery is in the left side of the boot under a cover. 

However I want to mention what my friend did to the car, on the advice of his dealer. My friend talked to his dealer about my concerns on the telephone. His dealer advised the following - start the car, put it in 'D', press the footbrake pedal, and at the same time press the accelerator pedal, rev the engine, and this will charge the 'battery'! My friend did this while I was present because I failed to find the 12v Battery! I was horrified at first because any automatic car I've known before would destroy the transmission by such a procedure! However, a screen display inside the car indicated that the engine was indeed charging a Battery, and my friend kept this practice going until all the bars on the Battery display on the screen had turned green. He then thanked me for my efforts and told me he would repeat this process every few weeks for the duration of his driving suspension! 

It later occurred to me both my friend and the dealer had mistaken my concerns about the 12v Battery for the hybrid Battery, and that my friend's practice of revving the engine in 'Drive' with the brakes on had recharged the hybrid Battery and had not done anything for the 12v Battery. I can only assume that the transmission was not destroyed because it is a robotized manual, and that keeping the brakes on must had disengaged the clutch. I have to say though, that I disliked the whole process. 

Returning to the 12v Battery, I assume that will still be in danger of discharging, especially if the car goes nowhere for six months and keeps getting crank started to recharge the hybrid Battery, which I see as not important at this stage. I've found an online PDF manual and from that, found instructions for starting a car with a discharged 12v Battery by using another 12v Battery and jumper cables, connecting to a dedicated positive 'jumper terminal' under the fuse box lid under the bonnet, and using an earthing point for the negative jumper cable, which appears to be a metal shield at the side of the engine in the illustrations. I am wondering if these are safe connection points for a 'smart' trickle charger like I have, and should I contact my friend again, and try to convince him that he needs to keep his 12 v Battery healthy, and not run the car in 'Drive' with the brakes on! 

[Herbie]

Quite simply connect the trickle charger, plug it in at the mains, switch it on and forget about it for six months.

It doesn't matter whether you connect to the Battery in the back or the jump-start point in the fusebox at the front because 12V is 12V and they're directly connected to each other anyway.

The negative clamp can either go directly on the negative Battery post or to any bare metal such as a bolt, nut, screw, bracket or whatever. As long as it's bare and not painted, it'll do the job. The only reason we're told not to connect directly on the negative Battery post is because a Battery can emit hydrogen gas so there's a risk of explosion from sparks igniting the gas. Personally I've never seen, witnessed or heard of this happening and neither have any friends in nearly 50 years of driving/hobby spannering. However, you can rest assured that from an electrical point of view, it makes not one jot of difference where you place the jump leads/charger leads as long as you get the polarity correct.

As for revving the engine with a foot on the brake, that is indeed a recognised procedure* and you won't damage the auto box because they don't have one. They use an electronically controlled variable transmission or e-CVT. One of the main components of this is what Lexus/Toyota call a 'Power Split Device' which is a constantly meshed planetary gearset.

*This is indeed for the traction Battery and is a procedure that Lexus technicians do when carrying out the Hybrid Health Check. Also, apps such as 'Hybrid Assistant' and 'Dr. Prius' ask you to do this very thing too.

[Lexusjim]

I believe the Battery in the ES is an AGM type (Absorbent Glass Mat) and needs a special type of charger......your charger should have details on it as to what type of batteries it can manage....

[Lexusjim]

Here are a couple of previous forum posts which may be of help

 

 

 

 

[mickdupleD]

On 8/28/2024 at 4:42 PM, Herbie said:

Quite simply connect the trickle charger, plug it in at the mains, switch it on and forget about it for six months.

It doesn't matter whether you connect to the battery in the back or the jump-start point in the fusebox at the front because 12V is 12V and they're directly connected to each other anyway.

The negative clamp can either go directly on the negative battery post or to any bare metal such as a bolt, nut, screw, bracket or whatever. As long as it's bare and not painted, it'll do the job. The only reason we're told not to connect directly on the negative battery post is because a battery can emit hydrogen gas so there's a risk of explosion from sparks igniting the gas. Personally I've never seen, witnessed or heard of this happening and neither have any friends in nearly 50 years of driving/hobby spannering. However, you can rest assured that from an electrical point of view, it makes not one jot of difference where you place the jump leads/charger leads as long as you get the polarity correct.

As for revving the engine with a foot on the brake, that is indeed a recognised procedure* and you won't damage the auto box because they don't have one. They use an electronically controlled variable transmission or e-CVT. One of the main components of this is what Lexus/Toyota call a 'Power Split Device' which is a constantly meshed planetary gearset.

*This is indeed for the traction battery and is a procedure that Lexus technicians do when carrying out the Hybrid Health Check. Also, apps such as 'Hybrid Assistant' and 'Dr. Prius' ask you to do this very thing too.

Unfortunately my friend would be unable to leave his Lexus on trickle charge indefinitely simply because he is storing it outside, and would have to connect a charger to either a house or garage socket through an open door or window. I've never seen inside his integral garage but I'd imagine it is full of household items like most people's garages! Thanks for the confirmation info on the 'brake and throttle' technique of charging the hybrid Battery. I didn't know the RC300h specifically had a CVT - very recently I've had experience with an 11 year old Peugeot automatic that uses an automated 'manual' box - it is obvious that a clutch engages and drive is taken up as soon as the footbrake is released. Apart from if you are on a gradient when the car will roll backwards until you either press the throttle pedal or hold it against rolling back on the handbrake... also I've got a lot of experience with automatic lorries that use similar gearboxes, and not torque converters. Obviously a torque converter-type transmission would not have tolerated 10-15 minutes of being held on the brake with the engine being revved, like my friend's Lexus did! 

The only reason I was wary of using an earthing point for a charger rather than the negative terminal of a Battery is because I have read somewhere (possibly Car Mechanics magazine, possibly somewhere else) that cars with Stop-Start, like my own diesel Volvo, may experience a malfunction of that system if a Battery charger is connected up to the positive and negative terminals of the Battery. I do not remember the reason why being gone into in detail - I just assume electronic software, which modern cars are crammed with, can be very finicky and easily upset, so when I wanted to maintain the Battery on my own car while it wasn't being used much, I chose to use a metal bolt under the bonnet as an earth, and I never had a problem. Last time I was at my friend's house, he reckoned the RC300h didn't have a stop-start function - though I imagine the petrol engine will start and stop as the software so wishes, in order to transition between electric and ICE power. 

[mickdupleD]

On 8/28/2024 at 10:29 PM, Lexusjim said:

I believe the battery in the ES is an AGM type (Absorbent Glass Mat) and needs a special type of charger......your charger should have details on it as to what type of batteries it can manage....

My own Battery charger, which I was going to loan to my friend (and may still do if I can persuade him it is a good idea) is branded Clarkes and was sold by Machine Mart, but it is indeed suitable for Absorbent Glass Mat and Enhanced Flooded Battery types.  CB09-6/12.

[Herbie]

23 minutes ago, mickdupleD said:

cars with Stop-Start, like my own diesel Volvo, may experience a malfunction of that system if a battery charger is connected up to the positive and negative terminals of the battery.

I have no idea why that should cause a problem but it doesn't apply here anyway, because hybrids are not 'stop-start' cars. Hybrids are a completely different technology and they don't have starter motors or alternators either. A conventional car starter motor will take up to 300A to crank the engine but our hybrids only need around 20A to boot the computers and make the magic happen.

Right at the beginning of the process there are two 12V relays working as a safety interlock. As long as the 12V Battery has enough power when the 'Start' button is pressed it will operated those relays, thereby 'giving access' to the hybrid system, which will be up and running when you get the green 'READY' light. The petrol engine may not necessarily fire up straight away but when the hybrid system wants it to run, it'll energise MG1 (Motor/Generator 1) and use that to spin the engine up to 1,000rpm before supplying fuel and a spark to ignite it. The hybrid system will then turn the engine on/off as and when it sees fit.

Some interesting stuff about the e-CVT or Power Split Device here.

[ColinBarber]

If you were leaving a Lexus hybrid for six months I would firstly make sure the hybrid traction Battery did have at least 50% charge by using the method you described and either connect a trickle charger or just disconnect the 12v Battery. Otherwise you would need to put the vehicle into Ready mode for an hour each week just to let the car recharge the 12v Battery before it gets too flat.

[NemesisUK]

Follow Lexus maintenance advice given in this doc.

 

Maintenance of hybrid battery.pdf

[Duggie B]

Maybe try a solar charger hooked up to the OBD socket 🤔 ?

[Linas.P]

On 8/28/2024 at 3:58 PM, mickdupleD said:

I have an elderly friend with a Lexus RC300h and he is unable to drive it for six months due to having had a heart operation. He has covered the car up on his driveway. I was concerned that the 12v battery may discharge over time, due to alarms and immobilizers. I have a 'smart' battery charger and wanted to loan it to my friend, to periodically top up the 12v battery. He allowed me to look at his car, but I knew nothing about the RC300h at the time. My own car is a Volvo with a front mounted battery, and to trickle charge that, I connect the +ve charger clamp to the +ve battery terminal, and the -ve clamp to an earth point, and it charges fine. This is what I expected to do on the Lexus, but initially I could not find the 12v battery, and my friend's Lexus handbook was very little help! 

I have since discovered from online sources the 12v battery is in the left side of the boot under a cover. 

However I want to mention what my friend did to the car, on the advice of his dealer. My friend talked to his dealer about my concerns on the telephone. His dealer advised the following - start the car, put it in 'D', press the footbrake pedal, and at the same time press the accelerator pedal, rev the engine, and this will charge the 'battery'! My friend did this while I was present because I failed to find the 12v battery! I was horrified at first because any automatic car I've known before would destroy the transmission by such a procedure! However, a screen display inside the car indicated that the engine was indeed charging a battery, and my friend kept this practice going until all the bars on the battery display on the screen had turned green. He then thanked me for my efforts and told me he would repeat this process every few weeks for the duration of his driving suspension! 

It later occurred to me both my friend and the dealer had mistaken my concerns about the 12v battery for the hybrid battery, and that my friend's practice of revving the engine in 'Drive' with the brakes on had recharged the hybrid battery and had not done anything for the 12v battery. I can only assume that the transmission was not destroyed because it is a robotized manual, and that keeping the brakes on must had disengaged the clutch. I have to say though, that I disliked the whole process. 

Returning to the 12v battery, I assume that will still be in danger of discharging, especially if the car goes nowhere for six months and keeps getting crank started to recharge the hybrid battery, which I see as not important at this stage. I've found an online PDF manual and from that, found instructions for starting a car with a discharged 12v battery by using another 12v battery and jumper cables, connecting to a dedicated positive 'jumper terminal' under the fuse box lid under the bonnet, and using an earthing point for the negative jumper cable, which appears to be a metal shield at the side of the engine in the illustrations. I am wondering if these are safe connection points for a 'smart' trickle charger like I have, and should I contact my friend again, and try to convince him that he needs to keep his 12 v battery healthy, and not run the car in 'Drive' with the brakes on! 

Funny enough, this was the point at which I decided to sell my RC - since covid I started mostly working from home and not driving much, to the point where I started worrying that my 12V Battery may go flat, had to go to the car to start it every other week and realised that if I am having to do this, then I don't need the car. 

I was about to start mocking people for not reading user manuals (I wonder why Lexus even bothers to print them in such good quality), but I do realise it is not your car and you just trying to help. Just saying - the starting point here should have been user manual. You did good job turning all the way to page 334 to find correct terminals for jump starting the car. They would also work for trickle charging, simple reason why the car even has these points is to prevent people from jumping the car backwards and blowing whole electrical system... so they simply provided different connection points that have fuses on them, but positive still goes to positive and negative still goes to negative, so not only they are safe, but they are preferable for this use.

Now second part is the one which I don't believe is explained sufficiently in user manual. All Lexus Hybrids have what is called "READY" mode/status, basically when you get into normal auto, you press the brake and start button and car starts idling in P position. In hybrid with CVT, the engine may not necessarily start, but it will simply state "READY" on the dash and engine will remain off, but you can drive off on EV mode, or engine may eventually start if you switch on air-conditioning or heating, or create other conditions that may need engine to be on. However, what manual does not say (at least I was not able to find it) what those conditions are. One of them is charge level of 12V Battery, meaning that to maintain 12V Battery one simply needs to get into the car, press brake, press start button and wait for "READY" to appear on the dash. Once it is there, that means car did all checks necessary including, making sure that 12V Battery is charged. If it is not charge the engine will start itself, no need to put it into D and rev the engine like Dealer suggested. I am not sure if revving the engine speeds-up charging of "traction" Battery, but it certainly charges 12V Battery. For that I don't even need user manual - hybrids still have normal engine, with normal alternator, so if engine is running, then 12V Battery is charging. Again the only issue here - hybrid engines may not start right away, hence it is important to check that "READY" symbol on the dash... but as long as it is displayed... car doesn't need anything else, all the systems are optimal and batteries are charged sufficiently to stay healthy. What that "sufficient" means is questionable, but I would say 1 week - 2 weeks should be safe. 

In short - he does not need to sit there revving the engine and charging traction Battery to full, traction Battery doesn't even meant to be full, it still has to have some capacity left for regen braking etc. I am sure that it meets and exceeds the time required to charge the 12V Battery, but it isn't even necessary, he only need to to press Brake + Start and then leave the car for few minutes until it shows "READY" on the dash, the engine may start by itself and that is normal. 

[Juicedrinker]

10 hours ago, Linas.P said:

Funny enough, this was the point at which I decided to sell my RC - since covid I started mostly working from home and not driving much, to the point where I started worrying that my 12V battery may go flat, had to go to the car to start it every other week and realised that if I am having to do this, then I don't need the car. 

I was about to start mocking people for not reading user manuals (I wonder why Lexus even bothers to print them in such good quality), but I do realise it is not your car and you just trying to help. Just saying - the starting point here should have been user manual. You did good job turning all the way to page 334 to find correct terminals for jump starting the car. They would also work for trickle charging, simple reason why the car even has these points is to prevent people from jumping the car backwards and blowing whole electrical system... so they simply provided different connection points that have fuses on them, but positive still goes to positive and negative still goes to negative, so not only they are safe, but they are preferable for this use.

Now second part is the one which I don't believe is explained sufficiently in user manual. All Lexus Hybrids have what is called "READY" mode/status, basically when you get into normal auto, you press the brake and start button and car starts idling in P position. In hybrid with CVT, the engine may not necessarily start, but it will simply state "READY" on the dash and engine will remain off, but you can drive off on EV mode, or engine may eventually start if you switch on air-conditioning or heating, or create other conditions that may need engine to be on. However, what manual does not say (at least I was not able to find it) what those conditions are. One of them is charge level of 12V battery, meaning that to maintain 12V battery one simply needs to get into the car, press brake, press start button and wait for "READY" to appear on the dash. Once it is there, that means car did all checks necessary including, making sure that 12V battery is charged. If it is not charge the engine will start itself, no need to put it into D and rev the engine like Dealer suggested. I am not sure if revving the engine speeds-up charging of "traction" battery, but it certainly charges 12V battery. For that I don't even need user manual - hybrids still have normal engine, with normal alternator, so if engine is running, then 12V battery is charging. Again the only issue here - hybrid engines may not start right away, hence it is important to check that "READY" symbol on the dash... but as long as it is displayed... car doesn't need anything else, all the systems are optimal and batteries are charged sufficiently to stay healthy. What that "sufficient" means is questionable, but I would say 1 week - 2 weeks should be safe. 

In short - he does not need to sit there revving the engine and charging traction battery to full, traction battery doesn't even meant to be full, it still has to have some capacity left for regen braking etc. I am sure that it meets and exceeds the time required to charge the 12V battery, but it isn't even necessary, he only need to to press Brake + Start and then leave the car for few minutes until it shows "READY" on the dash, the engine may start by itself and that is normal. 

@mickdupleD, @Linas.P'hybrids still have normal engine, with normal alternator, so if engine is running, then 12V Battery is charging', Hello Linus, I think you need to leave the vehicle in ready status for a good period of time (eg an hour) to get a boost into the 12v Battery because Hybrids do not have a normal alternator but a DC to DC converter.  I may be wrong but think that this is the way to guarantee 12v Battery stays fresh / full (correct me if I am wrong).  Of course the other issue is you really need to get all cars lubricants up to working temperature / fully circulating every few weeks and move it back and forth to save flat spots on the tyres and brake disk corrosion.  Is it left in Park with foot brake not engaged but blocks under wheels?  I would NEVER leave footbrake / handbrake on a stationery vehicle for periods of time as will seize at some point.  I used to run my MX5 every 1-2 weeks for a few miles throughout winter to keep transmission oil, lubricants / everything moving / mobile and engine, pipes etc operational.

[Linas.P]

15 minutes ago, Juicedrinker said:

@Linas.P'hybrids still have normal engine, with normal alternator, so if engine is running, then 12V battery is charging', Hello Linus, I am not sure if it will charge as a regular ICE engine because Hybrids do not have a normal alternator but a DC to DC converter.  I may be wrong but don't think the 12V battery would charge up i the way it does with an ICE engine (correct me if I am wrong) 

You are correct, it is not alternator at the front of the engine driven by belt like in regular car, so it is not exactly "normal alternator", but when ICE engine is running on hybrid the 12V Battery is charging "like in regular car".

Also correction - Lexus says "leave it in READY mode for 60 min", not sure if they playing safe here, as my understanding is... the engine will start, the engine will run until Battery is charged... then you can turn-off the car. There are no circumstances where engine has started, ran for a bit, shut-off and Battery is still not charged, so 60 minutes seems little bit excessive, nor the specific thing to measure. 

https://mag.lexus.co.uk/lexus-hybrid-parked/

[ColinBarber]

30 minutes ago, Linas.P said:

There are no circumstances where engine has started, ran for a bit, shut-off and battery is still not charged,

This is incorrect. The petrol engine running and the charge state of the 12v Battery are unconnected. The petrol engine runs to charge up the hybrid/traction Battery and will shut down as soon as it has sufficient charge (and the engine has reached a safe operating temperature).

The 12v Battery is charged by the hybrid system once in Ready mode. It charges at a relatively low current so, depending on state of charge, you would need 60+ minutes to charge it up.

[mickdupleD]

11 hours ago, ColinBarber said:

This is incorrect. The petrol engine running and the charge state of the 12v battery are unconnected. The petrol engine runs to charge up the hybrid/traction battery and will shut down as soon as it has sufficient charge (and the engine has reached a safe operating temperature).

The 12v battery is charged by the hybrid system once in Ready mode. It charges at a relatively low current so, depending on state of charge, you would need 60+ minutes to charge it up.

I'm not sure if a statement I made in my original post has been overlooked re. charging the hybrid Battery with the engine running, but one of my big concerns, was over what my friend with the Lexus had been told to do by the dealer, and he did it while I was there. That is, press the footbrake, turn on the hybrid system, then rev up the petrol engine to charge the hybrid Battery with the transmission in DRIVE. A couple of people in the thread provided me with a PDF file issued to U.S. dealers with regard to maintaining a car in storage, prior to delivery. The procedure described in the file seems to tell you to press the brake and start the hybrid system with the transmission in 'P'. "Make sure 'P' is selected" it says. While I was at my friend's house a few weeks ago when he tried this, I asked more about what he had been told to do. Apparently a female service advisor on the phone said "I'm not really supposed to tell you to do this." My friend said "Why not?" The reply was "If your foot slips off the brake, it could cause a lot of damage." In fact there was a moment where while the Lexus was being 'charged' in DRIVE, with the foot brake and accelerator pedals  depressed, my own Volvo was nearly T-boned when my friend relaxed his pressure on the brake pedal, as I'd pulled onto his driveway across the front of his Lexus. The Lexus leapt towards my car. I very swiftly rolled it backwards out of the way after this, in case there was a repeat. There seems to be a contradiction over this method of charging the hybrid Battery between what my friend was told to do by the UK dealer, and what it says in the U.S. PDF file. 

[mickdupleD]

12 hours ago, Juicedrinker said:

@mickdupleD, @Linas.P'hybrids still have normal engine, with normal alternator, so if engine is running, then 12V battery is charging', Hello Linus, I think you need to leave the vehicle in ready status for a good period of time (eg an hour) to get a boost into the 12v battery because Hybrids do not have a normal alternator but a DC to DC converter.  I may be wrong but think that this is the way to guarantee 12v battery stays fresh / full (correct me if I am wrong).  Of course the other issue is you really need to get all cars lubricants up to working temperature / fully circulating every few weeks and move it back and forth to save flat spots on the tyres and brake disk corrosion.  Is it left in Park with foot brake not engaged but blocks under wheels?  I would NEVER leave footbrake / handbrake on a stationery vehicle for periods of time as will seize at some point.  I used to run my MX5 every 1-2 weeks for a few miles throughout winter to keep transmission oil, lubricants / everything moving / mobile and engine, pipes etc operational.

I wouldn't be too worried about tyres, since I used to take classic cars off the road over winter and once covered up in my garage they didn't move from about November to April. I mostly did used to use a humidity controlled bag though, and I did leave the parking brake off. 

[ColinBarber]

9 hours ago, mickdupleD said:

I'm not sure if a statement I made in my original post has been overlooked re. charging the hybrid battery with the engine running, but one of my big concerns, was over what my friend with the Lexus had been told to do by the dealer, and he did it while I was there.

Normally an owner doesn't have to concern themselves with the hybrid Battery. It is has a low self-discharge rate, is completely isolated when the vehicle is power off so nothing is consuming its energy, and the charge level indicator the driver sees in reality only represents about 60% of the total Battery capacity - there is a large buffer at the top and bottom end to protect the Battery and maintain performance even if the Battery degrades.

Once you are leaving the vehicle for 3+ months then you need to think about it. Using the method you describe will allow you to bring up the state of charge higher than the vehicle will normally do itself which gives you a few more months before you would need to repeat the procedure to charge it back up - but at that point you would want to start the engine to lubricate it, pump up the tyres, move the vehicle so you aren't creating permanent flat spots on the tyres etc.

The easiest solution where possibly is to put the vehicle into Ready mode every couple of months, let the engine start and once it stops then the hybrid Battery has enough charge to go another couple of months without issue.

The bigger issue is keeping the 12v Battery charged.

[Juicedrinker]

11 hours ago, mickdupleD said:

I wouldn't be too worried about tyres, since I used to take classic cars off the road over winter and once covered up in my garage they didn't move from about November to April. I mostly did used to use a humidity controlled bag though, and I did leave the parking brake off. 

Fair enough however due to my profession and tyres being a big part of it I am always very careful