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Hello everyone.My Battery keeps going flat when the car's been stood for three or four days,i know nothing about electrics.Can anyone sugest what the problem might be,i do know it's not the brand new Battery.Any help and advice will be much appreciated. cheers.

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Firstly, there should be a date stamp or label on it somewhere. You really need to find that because if it turns out to be old (as in, say, more than 8 or 9 years) then I'd bin it straight away and get a new one.

If it's a relatively new one then you need to give it an overnight charge so that you're starting tests from a (hopefully) good point and you'll need a multimeter to measure voltages. First, measure the 'standing voltage' and compare to this chart:

 

bvolts.png.2144df7a095ef634ac056a2fa3bcad9a.png

 

If, after an overnight charge it's 50% or less, then again I'd be binning it and buying a new one.

Assuming it's got a decent charge overnight and holding it, next you need to fire up the engine and measure the voltage at the Battery terminals to see what the alternator is squirting out, which should be between 13.5 and 14.5V. Anything less is pointing to a suspect alternator.

Assuming that the alternator is indeed squirting enough volts out you may have a parasitic drain, ie, something draining the Battery that shouldn't. There are plenty of videos on Youtube demonstrating how to find a parasitic drain so I'll not try to reinvent the wheel, but instead to say have a look here.

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At this time of year sounds like a Battery on it's way out, just take it to local Battery specialist, and get them to load test.  (or if you have homestart get the local breakdown boys out)

Only other thing that it might be is I recall seeing post in the past about boot light on syndrome, cannot recall exact details, and may have not even been the LS forum, but something along the lines of the boot is shut, the light thinks it's open.

If it is that one way to prove is remove the boot light.

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22 minutes ago, Herbie said:

Firstly, there should be a date stamp or label on it somewhere. You really need to find that because if it turns out to be old (as in, say, more than 8 or 9 years) then I'd bin it straight away and get a new one.

If it's a relatively new one then you need to give it an overnight charge so that you're starting tests from a (hopefully) good point and you'll need a multimeter to measure voltages. First, measure the 'standing voltage' and compare to this chart:

 

bvolts.png.2144df7a095ef634ac056a2fa3bcad9a.png

 

If, after an overnight charge it's 50% or less, then again I'd be binning it and buying a new one.

Assuming it's got a decent charge overnight and holding it, next you need to fire up the engine and measure the voltage at the battery terminals to see what the alternator is squirting out, which should be between 13.5 and 14.5V. Anything less is pointing to a suspect alternator.

Assuming that the alternator is indeed squirting enough volts out you may have a parasitic drain, ie, something draining the battery that shouldn't. There are plenty of videos on Youtube demonstrating how to find a parasitic drain so I'll not try to reinvent the wheel, but instead to say have a look here.

The batterys fine,fully charged when fitted goes flat,the altinator is brand new as well and throwing out 14.2v.The car is undergoing work,it's not being driven at the moment,there must be a drainage somwhere.Ps iv'e got another brand new Battery,that went flat.Something definately wrong.

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2 minutes ago, Cotswold Pete said:

At this time of year sounds like a battery on it's way out, just take it to local battery specialist, and get them to load test.  (or if you have homestart get the local breakdown boys out)

Only other thing that it might be is I recall seeing post in the past about boot light on syndrome, cannot recall exact details, and may have not even been the LS forum, but something along the lines of the boot is shut, the light thinks it's open.

If it is that one way to prove is remove the boot light.

Batt brand new last week,also have another new batt that went flat.Good point about the boot light,ill look into that.cheers.

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2 hours ago, lazzlo amundo said:

Hello everyone.My battery keeps going flat when the car's been stood for three or four days,i know nothing about electrics.Can anyone sugest what the problem might be,i do know it's not the brand new battery.Any help and advice will be much appreciated. cheers.

Make sure that nothing is left in the cigarette lighter socket as a previous owner may have modified it so that it remains live whilst the ignition is switched off.

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13 minutes ago, royoftherovers said:

Make sure that nothing is left in the cigarette lighter socket as a previous owner may have modified it so that it remains live whilst the ignition is switched off.

No,theres nothing in the cigarette lighter socket,not even a cigarette lighter.

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1 minute ago, lazzlo amundo said:

No,theres nothing in the cigarette lighter socket,not even a cigarette lighter.

Then check that boot light and ALL interior lights are switched off.

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1 minute ago, royoftherovers said:

Then check that boot light and ALL interior lights are switched off.

I'll check tomorrow,gonna watch the link that Herbie posted.

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2 hours ago, lazzlo amundo said:

The car is undergoing work,it's not being driven at the moment

Mechanic leaving the door or boot open when they go home at night?

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8 minutes ago, Herbie said:

Mechanic leaving the door or boot open when they go home at night?

No,it's me.I do all my own work.

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I know you like to do all your own work but, if it continues, it might be worth getting a really good auto electrician to have a look. I had a similar problem and it turned out to be a tracking device - fitted when the car was new but, supposedly, deactivated - that was draining the Battery if I left the car for more than four days.

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47 minutes ago, Tulpen said:

I know you like to do all your own work but, if it continues, it might be worth getting a really good auto electrician to have a look. I had a similar problem and it turned out to be a tracking device - fitted when the car was new but, supposedly, deactivated - that was draining the battery if I left the car for more than four days.

Yes if i can't find the fault,an auto electrician it is.That's a good idea about a tracker.I cant do anything until tomorrow only watch youtube vids.

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On my mark 4 the culprit was the phone - it doesn’t switch off with the ignition- check yours if you have one 

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2 hours ago, cruisermark said:

On my mark 4 the culprit was the phone - it doesn’t switch off with the ignition- check yours if you have one 

Same for my MK4.

 

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Found the culprit,under the bonnet 10amp fuse Dome.I presume dome means dome light,but its also for the central locking.

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13 hours ago, cruisermark said:

On my mark 4 the culprit was the phone - it doesn’t switch off with the ignition- check yours if you have one 

Theres no phone,the workings are still there in the arm rest.

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1 hour ago, lazzlo amundo said:

Found the culprit,under the bonnet 10amp fuse Dome.I presume dome means dome light,but its also for the central locking.

You may have found the circuit causing the problems but I'm not sure you've found the cause. The dome light comes on when a door is open but you said that no doors were left open and the central locking on its own should not drain the Battery, especially a brand new one, over three or four days - so what's actually causing the drain from that circuit?

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49 minutes ago, Herbie said:

You may have found the circuit causing the problems but I'm not sure you've found the cause. The dome light comes on when a door is open but you said that no doors were left open and the central locking on its own should not drain the battery, especially a brand new one, over three or four days - so what's actually causing the drain from that circuit?

Herbie,i just don't know.There is a few things on that fuse.Mirrors,central locking,they'r ok thou.I dont know what else is on that fuse,the boot light doesent work the bulb seems fine but iv'e not got a spare one of that type yet.I'm hoping it's the boot light or somthing simple.No i haven't found the cause,i need a to find a wiring diagram.

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2 hours ago, Herbie said:

You may have found the circuit causing the problems but I'm not sure you've found the cause. The dome light comes on when a door is open but you said that no doors were left open and the central locking on its own should not drain the battery, especially a brand new one, over three or four days - so what's actually causing the drain from that circuit?

Herbie,it's a big list on that fuse.

iiterior lights,

personal lights'

door coursety lights'

ign switch light,

open door warning light,

boot light,

sun roof,

radio,

cd player.

preset steering system,

seat belt warning light,

air con,

rear view mirror,

door lock and theft deterrent system foot light,

electric mirrors,

locking with wireless remote system,i haven't got that key with it on.

Last but not least,automatic light control system

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Cliff, 

That's the list supplied by Lexus but it doesn't tell you if any thing has been added and uses that power source.

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39 minutes ago, Tulpen said:

Cliff, 

That's the list supplied by Lexus but it doesn't tell you if any thing has been added and uses that power source.

you mean like added electrical gadgets,it's a standered car.I thought if i tested the things on the list,i might find the problem.Somthings not right,it's been stood for 4 or 5 years.I would check all the earth leads,if i knew where they was.

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Remove the "dome" fuse and connect a multi meter set to 20 amps to start with across the connections where the fuse fits. Turn down the current range until you are using a range that is just above the current being drawn.
With the car doors closed, and ignition off remove, and replace  the fuses controlling the systems in the list noting any fall in the reading on the meter. This will show where the problem(s) lies. The maximum standing current should be around 20 ma  (20/1000 of an amp).

The dome fuse feeds many fuses down stream of it'self.

John.

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12 minutes ago, Britprius said:

Remove the "dome" fuse and connect a multi meter set to 20 amps to start with across the connections where the fuse fits. Turn down the current range until you are using a range that is just above the current being drawn.
With the car doors closed, and ignition off remove, and replace  the fuses controlling the systems in the list noting any fall in the reading on the meter. This will show where the problem(s) lies. The maximum standing current should be around 20 ma  (20/1000 of an amp).

The dome fuse feeds many fuses down stream of it'self.

John.

My head's done in,theres a few things on the list that are not working as i know of,all my fuses are ok so i don't know why they don't work.When i check them all tomorrow,i'm sure i'll find more things not working.Dash board warning lights dont work,seat belt warning light,door open warning,radio,all not working,all fuses good.There is only two fuse boxes isn't there,the main one under the bonnet and the one under the drivers footwell.

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There seems to be some confusion as you were asking about the Battery discharging over a 4 day period. Hence my above reply.

According to the wiring diagram in common with many Toyota/Lexus cars the is a multiple link strip fuse mounted in the side of the fuse box. This link is easily overlooked. and is difficult to change or see. On the LS 400 it contains 3 fuse links rated at 150 amp, 100 amp, and 30 amps. One or more links typically blow when reverse polarity jump starting has taken place. This is not a plug in fuse.

John.

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