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Battery drains overnight


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2007 Lexus RX 400h 3.3l SE CVT

Just love this car, but this fault is really annoying. I bought the car in April '19.  As winter approached, I notice that the Battery was not holding its charge. So, decided that a new Battery was the right way to go. All was well for several months, but now this (now 2 year) old Battery is discharging overnight, having been fully charged the day before (with a charger). I have seen several postings about this problem on Youtube. A lot of complaining, but no solution.

Is anyone any further forward with this irritation?

 

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Have you let it discharge and then sit there for a while, i.e., parked up for days on end and then only short runs? They don't like those scenarios and that would certainly contribute towards a Battery dying before its time.

If you feel that it really is down to a fault causing a parasitic drain, the video below shows the best way to go about tackling this problem.

Just remember that the car will always draw some current to keep the alarm alive, the radio stations in memory, to keep the clock at the right time and so on. This is called the quiescent current and around 50 milliamps (50mA or 0.05A) is considered to be normal.

 

 

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If you have let the voltage in the Battery fall too low, it may well charge up but you will have hastened it being unable to hold it's charge.  Also, overcharging a Battery (Too long and too high amperage) will also reduce its ability to hold a charge and shorten its life.  Best to use a suitable smart charger.  Is the Battery a cheapo?  It could also be a parasitic discharge as previously detailed.

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Yep, welcome to the rxh00h problem. 2 years is about right and it needs a new Battery. They are so small that anything discharges them. I have one of these in the car to start it https://www.ebay.co.uk/itm/393205362280?hash=item5b8cddae68:g:BboAAOSw9hBgVHeT 

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On 11/27/2021 at 11:41 AM, Nigel Perry said:

2007 Lexus RX 400h 3.3l SE CVT

Just love this car, but this fault is really annoying. I bought the car in April '19.  As winter approached, I notice that the battery was not holding its charge. So, decided that a new battery was the right way to go. All was well for several months, but now this (now 2 year) old battery is discharging overnight, having been fully charged the day before (with a charger). I have seen several postings about this problem on Youtube. A lot of complaining, but no solution.

Is anyone any further forward with this irritation?

Had the same problem with our new 2007 RX400h. Dealer replaced - twice- the Battery under warranty. Finally after about a year they fitted a Solar Panel Charger in the rear window. No further Battery issues up to when we traded it in for a RX450h in 2014.

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35 minutes ago, Russell Wheeler said:

Yep, welcome to the rxh00h problem. 2 years is about right and it needs a new battery. They are so small that anything discharges them.

It's not so much a 'small battery' issue as a usage issue. Whether it's a big 100Ah or a small 40Ah, the capacity should have no bearing on the longevity of the Battery, which should run to well over two years these days.

The problem is that people either don't use the car enough or only use it for short runs and, if that is indeed its usage pattern then a trickle charger should be used when it's parked up.

I don't know what capacity Battery the RX400h uses but let's say 45Ah and let's assume that it's brand new and fully charged. If we take the quiescent current as being 50mA (0.05A) like I said above:

45Ah means it can supply 45A for 1 hour, or 22.5A for 2 hours and so on.

45Ah / 0.05A = 900 hours or 37.5 days or 5 weeks 1 day from fully charged to fully discharged 

Remember though,

  • this example assumes a brand new and fully charged Battery, which obviously won't be the case in the real world
  • a hybrid takes about 20A to reach READY mode so in reality the Battery will not be able to start the car well before it becomes fully discharged, so we lose some time there
  • for various reasons the car charging system is nowhere near as good as an external charger so a 'half-hour blast' won't do anything to top up the battery; it would need to be a couple of hours at least

Hardly scientific and perhaps not even a good example, but I hope it gives some sort of indication that you can't really leave cars stood around doing nothing for extended periods of time, or only do short runs, without the risk of the Battery letting go.

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31 minutes ago, Herbie said:

It's not so much a 'small battery' issue as a usage issue. Whether it's a big 100Ah or a small 40Ah, the capacity should have no bearing on the longevity of the battery, which should run to well over two years these days.

The problem is that people either don't use the car enough or only use it for short runs and, if that is indeed its usage pattern then a trickle charger should be used when it's parked up.

I don't know what capacity battery the RX400h uses but let's say 45Ah and let's assume that it's brand new and fully charged. If we take the quiescent current as being 50mA (0.05A) like I said above:

45Ah means it can supply 45A for 1 hour, or 22.5A for 2 hours and so on.

45Ah / 0.05A = 900 hours or 37.5 days or 5 weeks 1 day from fully charged to fully discharged 

Remember though,

  • this example assumes a brand new and fully charged battery, which obviously won't be the case in the real world
  • a hybrid takes about 20A to reach READY mode so in reality the battery will not be able to start the car well before it becomes fully discharged, so we lose some time there
  • for various reasons the car charging system is nowhere near as good as an external charger so a 'half-hour blast' won't do anything to top up the battery; it would need to be a couple of hours at least

Hardly scientific and perhaps not even a good example, but I hope it gives some sort of indication that you can't really leave cars stood around doing nothing for extended periods of time, or only do short runs, without the risk of the battery letting go.

It's a PIA. I used mine Monday, did 70 miles, come to use it today, flat had to be jumped. I have a solar panel, which seemed to work ok in Summer. No other cars I have owned in the last 30 years have this problem and could be left a week without getting a flat Battery.  The Battery is less than 12 months old.

 

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2 hours ago, Russell Wheeler said:

It's a PIA. I used mine Monday, did 70 miles, come to use it today, flat had to be jumped. I have a solar panel, which seemed to work ok in Summer. No other cars I have owned in the last 30 years have this problem and could be left a week without getting a flat battery.  The battery is less than 12 months old.

 

Then your Battery is faulty or you have an electric parasitic drain fault on the vehicle. My 400h original Battery lasted 8 years before I noticed it getting weak and replaced it, and the vehicle could be left for 2+ weeks without issue.

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4 hours ago, Russell Wheeler said:

This looks a good price and a good capacity - 20,000 mAh. But being unbranded, I wonder how long have you had it in the car?

And how long does it stay fully charged? Are you using it to jump start the car? Do you think it's sturdily and safely made?

Sorry for the list of questions but I'll probably buy one if you can recommend it.

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On 11/28/2021 at 8:03 PM, Thackeray said:

This looks a good price and a good capacity - 20,000 mAh. But being unbranded, I wonder how long have you had it in the car?

And how long does it stay fully charged? Are you using it to jump start the car? Do you think it's sturdily and safely made?

Sorry for the list of questions but I'll probably buy one if you can recommend it.

I have had it about 12 months. I don't know how long it would remain charged, as it gets used as a 12v supply to pump up air beds, as a power pack to charge up mobiles etc, so I have never left it long enough to discarge on it's own. It does seem to work fine, I have also jump started a number of non hybrid cars, as well as the lexus with it. For the size of it, it is very powerful

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Not a solution your Battery problem, unfortunately.  But some time ago I invested in a NOCO Power Pack just in case I was caught with a flat Battery and no time to use the trickle charger.

Knowing you have one in the boot will at least ensure that you’re never going to be stuck - provided, of course that it’s very occasionally recharged!

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1 hour ago, Russell Wheeler said:

 

And posting that (without explanation or context) achieves what exactly Russell?

I'm assuming you're attempting to back up your theory that there's a problem with the RX400h 12V Battery?

I suppose there are two possibilities:

  • There is a real, actual, parasitic drain on the system. Have you investigated this?
  • The only thing wrong is actually a design problem in that Toyota/Lexus specified a low capacity 12V Battery

Given that the RX400h ceased production in about 2008 (latest I've seen registered is 2009 with the RX450h taking over from then), good luck with getting Toyota/Lexus to do anything about it now. The only options now are to either put up with it and plan for when it goes flat or you change the car because it doesn't fit your usage pattern. I suppose a third option would be to try to find a higher capacity Battery that physically fits in the Battery tray.

Quote

It's a PIA. I used mine Monday, did 70 miles, come to use it today, flat had to be jumped. I have a solar panel, which seemed to work ok in Summer [...]  The battery is less than 12 months old.

So you did 70 miles on Monday 22nd then didn't use the car again until Sunday 28th. How many miles did you do in the previous week, i.e., 15th to 22nd?

All batteries in all cars will go flat if not used, it's simply a matter of how long that takes.

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On 11/27/2021 at 11:41 AM, Nigel Perry said:

2007 Lexus RX 400h 3.3l SE CVT

Just love this car, but this fault is really annoying. I bought the car in April '19.  As winter approached, I notice that the battery was not holding its charge. So, decided that a new battery was the right way to go. All was well for several months, but now this (now 2 year) old battery is discharging overnight, having been fully charged the day before (with a charger). I have seen several postings about this problem on Youtube. A lot of complaining, but no solution.

Is anyone any further forward with this irritation?

 

Any updates, Nigel?

Hoping it's resolved now...

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