Battery draining overnight

Orion · August 15

About 7 years ago my wife and I bought two Lexus RX 400h, a 2005 and a 2008. We love the cars!

Over the years we have both had the same ongoing issue. From time to time, the smaller Battery dies overnight. We bought the modern small jump starter packs, so as to be ok.

The problem however goes on. Now, my wifes car (2005) has had 4 new batteries, mine has had just as many. Three weeks ago we got yet another new Battery (under warranty) the old one was 'knackered' to quote the guy.

Something must be draining these batteries. Obviously we have looked at all the usual suspects. We take great care to make sure that nothing is left on. At least nothing we can switch off.

The cars were not from one source, they are not identical in build. In every other way they are brilliant drives.

We use a Battery charger once in a while 'in case'.

We are both in our 70's and just want a quiet, reliable, stress free life.

One mechanic has suggested that her ASC is the cause. The ASC doesn't show any fault, it seems to work... though that is hard to know. He suggested pulling the fuse. I would if I could find it.

So, question is... what is happening to two cars? Also where is the ASC fuse?

Thanks in advance.

Peter

Malc1 · August 15

“ something must be draining ……”

It’s not good at all BUT I’m thinking that more modern day batteries are not manufactured to the same “ high quality “ standards as earlier …….. I say this because of the failings on my more recent ordinary 12v batteries on my Honda Legend …… failing within the warranty period …… twice …… supplied and re-supplied by courtesy of my RAC Breakdown Cover …… they must be fed up too or maybe it’s now so common it’s expected 🥵

Good luck getting to the bottom of it

Malc

Herbie · August 15

12 hours ago, Orion said:

So, question is... what is happening to two cars? Also where is the ASC fuse?

First of all, what is ASC?

Secondly, how often do you use the cars and for how long?

The 12V batteries are only small and have low capacity so they need to be used regularly and for decent runs - a round trip of 10 minutes to the local paper shop isn't going to cut it. If you aren't using them often enough or for long enough, the best solution is to keep each car on a trickle charger when they're not actively being used.

All cars have a current draw when they're 'asleep'. This is called the 'quiescent current' and it keeps alive things like the alarm, the clock, radio presets, seat memory and so on, and it should be somewhere in the region of about 50mA to 70mA.

The capacity of the Battery is measured by the Ah (AmpHour) rating. I don't know what yours are but we'll assume 50Ah, which means it can supply 50A for one hour; 25A for two hours; 12.5A for four hours and so on.

If the quiescent current draw is 50mA (0.05A) then 50Ah divided by 0.05A = 1,000 hours (41.66 days or 5.95 weeks) to go from fully charged to fully discharged if the car is left standing (assuming a brand new and fully charged battery).

This is a theoretical maximum and you'll never see it in reality. Also, the Battery will not be able to start the car long before it becomes fully discharged, so the practical useful time you get will be considerably less than the 5.95 weeks you see above.

If there's a fault somewhere and the Battery drains due to that, this is called a 'parasitic current draw' and it obviously needs to be fixed. Below is the best way I've ever seen for determining parasitic draw and tracing the fault:

Orion · August 16

Hi,

1. ASC is automatic stability control, I think this is what I call 'Traction Control'. Doesn't usually matter on dry roads.

2. The wife drives about 2 miles to work most days. I don't drive that much. Though we had this issue when we did do more driving.

I topped her Battery up yesterday. I was showing full charge and 14.2v. This morning I checked,it as down to 11.8v and 60% charge. I understand about amps, but have no way to measure them.

We have had numerous new batteries, and have 'upgraded' to "better quality" Bosch. They failed just as quick. They surely can't all be faulty?

I will try to follow that video,but don't currently have a tester. (Pun intended)

Herbie · August 16

1 hour ago, Orion said:

2. The wife drives about 2 miles to work most days. I don't drive that much. Though we had this issue when we did do more driving.

That is absolutely far too little. At the very least you need a good hour run.

1 hour ago, Orion said:

We have had numerous new batteries, and have 'upgraded' to "better quality" Bosch. They failed just as quick. They surely can't all be faulty?

What you have to appreciate is that this is not a 'fixable' fault and there's nothing anyone can do to rectify it. It's a design fault that should never have been approved during the drawing board stage and it's not a question of using a "better quality" Battery. The only option is to use a Battery with a higher AmpHour capacity but unfortunately that comes with a bigger physical size that doesn't fit in the Battery box.

ColinBarber · August 17

10 hours ago, Orion said:

ASC is automatic stability control, I think this is what I call 'Traction Control'. Doesn't usually matter on dry roads.

VSC, not ASC.

I don’t see why that would cause a Battery drain, it would be powered off with the vehicle. Do not disable it, it is there is help you out in an extreme situation such as collision avoidance, not just wet weather grip, and is intrinsically linked to ABS.

I suspect you have something else draining the Battery. Possible the Battery backup in the alarm system has failed and needs constant charging.

9 hours ago, Herbie said:

That is absolutely far too little. At the very least you need a good hour run.

I disagree. Using the vehicle daily, even for short runs is normally fine. It’s long periods of no use that is the issue. It would probably add up to an hour or more each week. My wife had a similar commute for a few years and her hybrids were fine.

GSLV6 · August 18

Regular short trips are not sufficient to keep the auxiliary Battery sufficiently charged so what happens over time is if allowed to drain below 70% or so, even leisure types, eventually it'll lose charging capacity as it can damage the cells. The hybrid Battery & inverter circuit contain the charger for the auxiliary Battery and really need a minimum of a 30 minute run once weekly to keep the auxiliary Battery sufficiently charged to prevent excessive drain down. A lexus tech told me that after I replaced mine for the second time in 5 years. Best thing is to hook up charging tail leads directly to the terminals and if only doing a few miles each day, to hook the charger up overnight for at least two days in the week. CTEK charges have a maintenance/desulphate cycle to recover deep discharged batteries and really do extend the life of a Battery considerably if regularly used. Infrequent trickle charging won't much help a battery's health. My motorbikes are both hooked up to chargers 50% of the year (I switch use between them) and are pretty much maintenance charged one in two weeks throughout the year. It's the only way to make them last more than 3 or 4 years (they're only 12AH!)

Madsod · August 18

When I had a 400H I used one of these solar panels, I found it really good when going on my 3 week holiday and meant I was able to get in and start my car without any worry about the alarm etc draining the power.

https://www.amazon.co.uk/Powered-Battery-Charger-Caravan-Package/dp/B07P7C6QLD/ref=sr_1_6?af=eyJxdWFydHpWZWhpY2xlIjoiMjktMTA1MTkifQ%3D%3D&crid=26NXWAUXZC9P1&dib=eyJ2IjoiMSJ9.yW__zO6Nl74VSNURd81s3QPpKRhGKgbn1FSiQC1vSIYbcfhWQiazIUA2gJD1otExHC1ijj9pek5QOBZ3xopkINXs4W0zG1l1QmfBTXfboUYx3Mc977DndFGfxkFZ-GVxLvpcr-FfixnJ8T4J3dQKccXQ4xn2pZLfvOotuX8_9ysWMk6uwnyAmlFVEkRWEyoccWJqeje-eXQO8FjlKe5E8622G8OG1251B-bzTOzHNJjRmdZxlxXvVfae6HW-KMrM6GM7xYDgTgxydDuU1rKZjcJ0v7OU1t0u7AaoBaAFHmQ._lpVIN5ia9S_f-CuuDn4nTpoVqygBJgGbowKMQph1V8&dib_tag=se&keywords=aa+solar+trickle+charger+for+car+battery&qid=1724012484&sprefix=Aa+solar%2Caps%2C88&sr=8-6

They can be purchased on other sites as well as Amazon…

Because it plugs in the OBD2 connector, I found it quite easy to plug in/unplug without lifting the bonnet each time, I rested the panel in the sunroof tray and it might be an option to leave your car Battery charging during the day when your not using the car and help prevent the issues you are facing.

it obviously won’t recover a flat Battery and you must unplug this before starting the car but otherwise I found it very useful.

My brother in law lives in North America and travels quite a bit so he plugs his in when he’s parked up at the airport for a few days during the winter, it just keeps the Battery slightly ‘warmer’ and prevents the cold weather killing it whilst he’s away.

stepheneric · August 18

1 hour ago, Madsod said:

When I had a 400H

2 hours ago, Madsod said:

solar panels,

We had a rx400h new in 2007 and had to have two new 12v batteries replaced in the first year (RAC came out a few times more than that) Eventually Lexus Derby

fitted free of charge a little solar panel (approx 9" x 4") in the rear window discreetly wired to the Battery We had no more problems with Battery failure in

the next six years of ownership.

brendangeorge · August 27

On 8/17/2024 at 8:25 AM, ColinBarber said:

VSC, not ASC.

I don’t see why that would cause a battery drain, it would be powered off with the vehicle. Do not disable it, it is there is help you out in an extreme situation such as collision avoidance, not just wet weather grip, and is intrinsically linked to ABS.

I suspect you have something else draining the battery. Possible the battery backup in the alarm system has failed and needs constant charging.

I disagree. Using the vehicle daily, even for short runs is normally fine. It’s long periods of no use that is the issue. It would probably add up to an hour or more each week. My wife had a similar commute for a few years and her hybrids were fine.

If the Battery discharges on the drive way over night you have a fault or a bad Battery.
I put a new bat in just after Christmas and regularly leave my car sitting for two weeks with no probs.
Over Christmas I left it for a month and the bat went flat - I charged it and it would only go to 75%. It still started the car OK - note it was the original 11 year old Battery.
Bren

ColinBarber · August 27

22 minutes ago, brendangeorge said:

If the battery discharges on the drive way over night you have a fault or a bad battery.

As explained by the OP, the Battery is new, and it isn't the first time it has had to be replaced.

brendangeorge · August 27

49 minutes ago, ColinBarber said:

As explained by the OP, the battery is new, and it isn't the first time it has had to be replaced.

Then you have a fault.

Greisingel · August 29

https://www.amazon.co.uk/Universal-Disconnect-Terminal-Isolator-Vehicles/dp/B075CK7W3Z/ref=pd_ci_mcx_mh_mcx_views_0?pd_rd_w=AJBMG&content-id=amzn1.sym.d63274d0-bf52-45e7-ae69-2bcf85c5865c%3Aamzn1.symc.ca948091-a64d-450e-86d7-c161ca33337b&pf_rd_p=d63274d0-bf52-45e7-ae69-2bcf85c5865c&pf_rd_r=DCVAV0JB0X4HYR6TBV85&pd_rd_wg=KEy6a&pd_rd_r=53d8f9de-97a0-416a-9612-5804d74ee81b&pd_rd_i=B075CK7W3Z

ColinBarber · August 29

6 minutes ago, Greisingel said:

https://www.amazon.co.uk/Universal-Disconnect-Terminal-Isolator-Vehicles/dp/B075CK7W3Z/ref=pd_ci_mcx_mh_mcx_views_0?pd_rd_w=AJBMG&content-id=amzn1.sym.d63274d0-bf52-45e7-ae69-2bcf85c5865c%3Aamzn1.symc.ca948091-a64d-450e-86d7-c161ca33337b&pf_rd_p=d63274d0-bf52-45e7-ae69-2bcf85c5865c&pf_rd_r=DCVAV0JB0X4HYR6TBV85&pd_rd_wg=KEy6a&pd_rd_r=53d8f9de-97a0-416a-9612-5804d74ee81b&pd_rd_i=B075CK7W3Z

Not ideal. You would be resetting the engine ECU so long term fuel trims need to be relearnt and you possibly have to go through a ISC reset procedure otherwise the hybrid system may not shut down the engine - affecting economy.

Best to identify the issue and resolve.

Greisingel · August 30

Yes – I agree. But if you were off to Spain for a fortnight – it might be an option. But you are right – only good if resetting a serious CEL issue as a short term fix or away for very long time.

Russell Wheeler · August 31

On 8/16/2024 at 10:36 PM, Herbie said:

That is absolutely far too little. At the very least you need a good hour run.

What you have to appreciate is that this is not a 'fixable' fault and there's nothing anyone can do to rectify it. It's a design fault that should never have been approved during the drawing board stage and it's not a question of using a "better quality" battery. The only option is to use a battery with a higher AmpHour capacity but unfortunately that comes with a bigger physical size that doesn't fit in the battery box.

I agree, I have a 2006 rx400 and only use it for longer runs a couple of times a month. Ended up putting on a disconnect switch on the Battery so it doesn't drain when left.