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RC F Sport 12v battery not holding charge.


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Bought an RC nearly 4 years ago and only use it occasionally. After about 13 months the 12v Battery started to go flat and left me waiting for the recovery service to bail me out. Lots of trips to the dealer they eventually changed the Battery and no more problems, until 4 months ago when it all started again. 

I am unable to leave the car for four days or it tells me " hybrid system stopped. put park brake to park" and refuses to start.

Before I start on at the dealer again I wondered if anyone else had the same problem. Any help would be appreciated. 

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Any possibility you can connect a CTEK charger for example? They are highly reccomended for Classic and Performance cars that ( unfortunately ) don’t get used on a regular basis.

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1 hour ago, BRYAN C said:

Bought an RC nearly 4 years ago and only use it occasionally. After about 13 months the 12v battery started to go flat and left me waiting for the recovery service to bail me out. Lots of trips to the dealer they eventually changed the battery and no more problems, until 4 months ago when it all started again. 

I am unable to leave the car for four days or it tells me " hybrid system stopped. put park brake to park" and refuses to start.

Before I start on at the dealer again I wondered if anyone else had the same problem. Any help would be appreciated. 

You’ve posted in the wrong sub section… this is the big boys F section 

youll get more responses via the RC300h fsport section 👍🏻

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1 hour ago, BRYAN C said:

Bought an RC nearly 4 years ago and only use it occasionally.

That right there is your problem............^^^^^^^^^^^^^^^^^^^

A conventional car will have a 12V Battery rated at something like 75Ah, quite probably more, to supply 300A plus to the starter motor.

Hybrids don't have a starter motor and only take about 20A to 'start' the car, ie, get it into READY mode. This was probably just one of the factors that drove Toyota/Lexus to fit lower capacity batteries of around 45Ah or even just 41Ah in their hybrids.

When parked up and unused, there is still a current draw from the Battery to feed the alarm, the clock, the radio presets and more. This is called the quiescent current and a figure of around 50mA is considered to be the norm. Plus, all batteries will self-discharge anyway, but we'll leave that out of the mix for now.

I don't know what capacity your Battery is but we'll use 45Ah for this example and we'll also assume that it's brand new and fully charged. 45Ah means that it can supply 45A for one hour or 22.5A for two hours and so on.

45Ah divided by 50mA (0.05A) = 900 hours or 37.5 days or 5.35 weeks between fully charged and fully discharged. Don't forget though, that for the purposes of starting the car, it will become useless and not be able to provide enough power long before becoming fully discharged.

In reality we may be looking at getting 4 to 4.5 weeks maybe? I don't know, it may be even less. And that's for a brand new, fully charged Battery. Look at one a couple of years old and the figures may be even lower.

So, you either have to use it more or keep a trickle charger on it.

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1 hour ago, BRYAN C said:

I am unable to leave the car for four days or it tells me " hybrid system stopped. put park brake to park" and refuses to start.

 

This seems a little unusual as if the 12v Battery were flat one wouldn't be able to open the car with the remote and there would be no display?

Your timescales are a little difficult to follow. Was that 13 months after you bought it i.e. nearly 3yrs ago? Everything was then ok for 2.5yrs and now you're having issues again?

As Herbs posts, you need to drive it more or leave it on trickle charge

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5 minutes ago, BRYAN C said:

Thanks for the replys, except for one. It seems when you spend £40+ it doesn't  guarantee you a battery that lasts for a week.

You got a Battery for £40? 

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11 minutes ago, NemesisUK said:

You got a battery for £40? 

If he did, that may well be his problem - but I rather suspect that he meant £40k+ for the car :whistling:

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5 hours ago, BRYAN C said:

Thanks for the replys, except for one. It seems when you spend £40+ it doesn't  guarantee you a battery that lasts for a week.

The standard Battery on the RCh is rated at 48 Ah (5 hours) which is about 56 Ah (with the more normal 20 hours test).

If we assume you have a 50 mA power draw when the vehicle is not be using, and at 30% state of charge you can no longer 'start' the vehicle, then the standard Battery will last about 4.5 weeks. Certainly we have members here that have left an IS300h/RC300h for three weeks and returned without an issue.

But the above is based on the Battery being in excellent condition and being fully charged when it is first left.

If you are using your vehicle occasionally then you are most likely not fully recharging the Battery and so it slowly discharges to the point where you can no longer start. The above uses figures of 8.4 Ah consumed per week, but to make things easier lets say 10 Ah and the point at which the Battery no longer can start the vehicle is with 20 Ah capacity left. Let's also assume you only put back in 5 Ah at the end of each week.

Week 0: 56 Ah starting capacity

Week 1: 56-10+5 = 51

Week 2: 51-10+5 = 46

Week 3: 46-10+5 = 41

Week 4: 41-10+5 = 36

Week 5: 36-10+5 = 31

Week 6: 31-10+5 = 26

Week 7: 26-10 = 16, cannot start to add back in 5 Ah.

At week 7 you encounter the situation where the vehicle cannot be left for a week without the Battery going flat but that is because of the previous 6 weeks slowly discharging the Battery.

 

What is also happening is that the Battery is being left for weeks in a discharged state which lead acid batteries don't like. Weeks 5 through 7 are damaging the Battery, shortening its life. Therefore when you recharge the Battery you probably don't have 56 Ah capacity and the vehicle only lasts 5.5 weeks rather than 6 weeks the next time.

 

All of this happens whether you have a hybrid vehicle or not. The difference is that for a normal petrol/diesel vehicle the Battery is larger and therefore week 7 may extend to week 12, but you still end up in the same place eventually.

 

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  • 3 weeks later...

During the COVID lockout, I used my 2019 RC300h far less than I usually do. Three times in 2 months, the Battery went dead.
I had to call Lexus support which, by the way, is very helpful and efficient.
The mechanics told me that this is a very common problem on Lexus hybrid cars, as they fitted with very limited Battery power.
I never had this problem before and reported it to my Lexus dealer. He was not at all surprised as it seems to be a common problem. He did confirm that Lexus hybrids have a smaller Battery. There is no real solution other than the dealer recommended that I start the car at least once a week, which I don't consider a very practical alternative.

My son-in-law had the same problem around this time on his IS300h.

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11 minutes ago, TeDClubLexus said:

There is no real solution other than the dealer recommended that I start the car at least once a week, which I don't consider a very practical alternative.

By this they mean put the car into the Ready state in Park and let the hybrid Battery recharge the 12v aux Battery. If the hybrid Battery get low on charge the petrol engine will fire up briefly to top up the charge.

Perfectly practical ....

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3 hours ago, TeDClubLexus said:

There is no real solution other than the dealer recommended that I start the car at least once a week, which I don't consider a very practical alternative.

Practical alternative to what?

You have four choices: use the vehicle as it was meant, use a Battery charger at least once a week to top up the Battery charge lost through normal self-discharge and the small drain the alarm/stereo/central locking systems consume, let the vehicle recharge the Battery by putting it in 'Ready' mode for at least an hour a week or put the Battery on permanent trickle charge.

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