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Sitting unused for 6 months .

steely dan

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2014 GS 450h F sport .

Car inherited by my wife in her new post , it's been sitting unused for 6 months . I tried to start it but 12v ignition Battery is flat .Connected smart charger to Battery in boot after disconnecting the neg connection and it wasn't having it ,charger says the Battery is fully charged. Followed the handbooks instructions to the letter  to jump start it via second vehicle with it's engine running but again no joy . When doing this and holding the brake pedal down it pushed back quite violently when start button engaged. 

Last time the car had any charge in the boot mounted Battery the alarm went off .

My question is how long does the main ( hybrid ) batteries hold sufficient charge to "start " the engine with a fully charged 12V ignition system Battery fitted ,and has the last alarm initiation immobilised the damned thing.......



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Hybrid batteries doesn't act in any way when starting the engine, so not sure if I answer our question, but if the 12v Battery is charged or replaced with new one, the engine should start regardless of hybrid Battery condition.

As mentioned... jump-starting any hybrid car is not good idea (generally, it is not safe on any new-ish car). Assuming this is company car, it should be covered with some kind of service plan etc. and possibly there is number to call somebody to sort out everything for you.

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I would double on that, even with best intentions it is little you can do to the car yourself and knowing the value of the car I wouldn't take risk to damage something by doing myself.

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I know very little about hybrids, nor would I want one, but the pictures above taken from the manual do seem to make it clear that it can be jump started, so why I'm wondering are people contradicting that?  

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I suspect it may have been a warning on that particular model as there isn't in my neighbours car. Even Lexus own 450h documentation says:

Long-term parking. If the vehicle has been parked for a long time, the 12-volt and the hybrid Battery will discharge gradually. For parking longer than about 30 days, charging of the 12-volt Battery may be required. Your Lexus dealer has details. To keep the hybrid Battery in good condition, drive the vehicle at least once every several months for at least 30 minutes or ten miles. If the hybrid Battery becomes fully discharged and the vehicle will not start, even with a jump start to the 12-volt Battery, contact your Lexus dealer.

If that manual is definitely from your model then I would go ahead with jump starting. 

Being Hybrid has nothing to do with being able to jump start it or not. If anything it would be some of the control electronics that could be susceptible to transient spiking, which is why some have dedicated jump start connections as there is a additional filtering on some. 

Does everything appear to power up when you had the smart charger on? Do you get any dash lights/warnings? These smart chargers aren't sometimes 100% accurate because of the way they try to measure the current. You could try manually charging the Battery with a good old fashioned charger, or leaving the jump leads on for a couple of minutes before actually trying to start the car.

All hybrid systems have a low voltage protection system but not sure on the 450 if that would disable the car starting completely. Usually there is a warning on the dash. The alarm won't permanently disable the vehicle, only when in triggered condition.

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Thanks for all your replies.

I relented and called the supplying dealer and spoke to a senior technician. 

The engine is started via one of two electric motors within the gearbox , these are powered from the hybrid batteries. The boot mounted 12V Battery powers the ignition circuitry inc. all required ECU's. 

The alarm would have initiated when the car was unlocked with a low voltage available at the ignition Battery.

This Battery can be only be trickle charged to full power hence my "smart" charger being confused.....

The violent push from the brake pedal is the brake booster response to low Battery condition.

The car can be jump started as correctly described in the manual above either by attaching the jump leads directly to the Battery or via the red plastic covered power point within the engine bay and a suitable earth point. 

The hybrid batteries should hold their charge for 12 months or more and if unfortunately they do lose their charge a special Lexus charger is required . This is so rare that even the supplying dealer hasn't got one and has to have it loaned from Lexus themselves .........

So , I'll connect a trickle charger to the ignition Battery and leave it for several days and then try it again. 



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