Mechanics

CAR BATTERY DRAINS

2002 Lexus IS 200 • 100,800 miles

I have a peculiar problem with my car. The battery drains off within 3 - 4 days. I drive the car for 600 miles to Norwich and the battery is completely charged. It drains off in 3-4 days. I checked for the output from the alternator. In idle condition the output varies from 14.02 - 14.01 Volts, When the RPM is raised the output is greater than 14.10 Volts. The battery is brand new from Lexus. There are no lights on. The music system is working perfectly fine. I do not have a light in the hood of the car casing the engine. The lights are all on manual mode and turned off. The light in the boot is switched off. The light in the glove bocx is switched off. To check if there is a drain I parked the car in the garage and didn't even enable the security alarm. I have done all the checks on my car but unable to find the problem. Also I did remove the main fuse and found my battery tto drain. Have taken to Lexux showroom a couple of time and the technicians are unable to rectify the problem. Pls help. I am sick of jump starting the car.
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Agnelocorrea
April 14, 2012.




The drop in voltage is not the drain but it is an indicator of the effects of the drain. Think of the water in a municipal water tower. The drain would be the water leaving the tank. That is current as in current in a river, and current in a wire. The RESULTS of that drain is the pressure in the tower would go down because there's less weight in the remaining water. Voltage is electrical pressure. As current flows through circuitry, the battery becomes discharged and the voltage goes down, so the voltage readings do have merit but there's more to the story.

Generally speaking we consider a battery to be fully charged when we find it at 12.6 volts, and fully discharged at 12.0 volts. You will often find higher than 12.6 volts right after charging it with a battery charger or by driving the car because some of the electrons haven't been absorbed into the plates. That's called the "surface charge" and must be removed for proper battery testing. That is done by turning on the head lights or anything similar for about ten seconds.

Even when just parking the car after driving it, that surface charge exists so in the case of the 12.69 volts, you can expect the voltage to drop a little as the electrons leave the acid and go into the plates. Typically the voltage will stay near 12.6 volts. 12.42 volts appears to be one third of the way to discharged and that is too fast over three days but those readings can be misleading, or at least inaccurate. Unless specified differently, the industry standard is a good battery will supply all the computer memory circuits and still be able to start the engine after sitting for three weeks. Going just by your voltage readings that means the battery will be too run down to crank the engine after nine days. That implies a drain of three times the allowable.035 amps, or roughly 0.1 amp. Most amplifiers draw more than that when they're on but not amplifying any signal so it should kill the battery in a few days. If you find the battery holds up considerably longer with the amp unplugged, that proves my assertion that the voltage readings do not accurately represent the drain. Just because it's down to 12.42 today, it may not drop another.27 volts in another three days.

Regardless of all my assumptions and observations, I'm hoping you found the cause. You originally said the battery would be dead in three or four days and that would fit with the typical amplifier staying on. The heat is a good clue too although if it does not get warm, it still could be staying on.

Caradiodoc
Jun 30, 2012.
Thank you very much for your response. Just to add a note on my analysis, I checked the drain in the battery by connecting an ammeter in series (i.E- The positive terminal of the Ammeter connected to the black wire of the car and com wire of the ammeter connected to the negative terminal of the battery). The max drain I get is 0.025A which is 25mA and is acceptable. Yesterday the voltage across the terminal was 12.51V and when I Checked it today morning it was 12.42 V. After writing my analysis I did have a check again and found that the voltage had fallen down to 12.28V. So now I think the

Tiny
Agnelocorrea
Jun 30, 2012.
Sorry for the incomplete message. So now I feel that the amp might not be an issue. Is there anyone on this planet who can tell me why the battery is draining so fast when the max drain current is 25mA max. Also This is a brand new Toyota 570EN battery.

Tiny
Agnelocorrea
Jun 30, 2012.
You might try disconnecting one battery cable, then monitoring the voltage periodically. I've never done that myself but I would expect that if the voltage still drops off, it's not really getting fully charged and you're measuring the surface charge. I built a lot of "bugged cars" for my students to diagnose and one was a single bad diode in the diode trio of an older GM generator. One of the clues they needed to find was under a load test, it could only produce 20 amps. That was one third of normal and enough to run the car but not much left over to recharge the battery. A harder-to-spot observation was that the system voltage actually was a little higher than normal. Even though voltage was higher, that didn't equate to fully charging the battery. Easy to explain; not so easy to diagnose without performing a load test.
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Caradiodoc
Jun 30, 2012.
The load test was done on the battery by Lexus and they have given me a report with the readings and it shows the bayyery is fully charged. Also after I drove 600 miles I parked the car for 24hrs without starting it and checked the battery to find the reading of 12.65V which means its fully charged. I will try by disconnecting the negative terminal and checking for the battery readings.

Tiny
Agnelocorrea
Jul 1, 2012.
Today I did some more tests. Disconnected the negative terminal at the battery end. Checked for the voltahe and found it to be 12.6V. As soon as I connected the negative terminal the voltage dropped to 12.42 volts in a matter of a min. Disconnected the negative terminal and connected a 12V bulb in series with the battery. Found the light in the bulb fluctuating. Now can you advise me where the problem might be.

Tiny
Agnelocorrea
Jul 1, 2012.
I did the following tests today. Disconnected the battery. Checked for the voltage actoss the terminals. The voltage was 12.6Volts. Connected the black terminal to the battery. Switched on the car. The reading was 14.27 - 14.28 Volts across the terminal and the current drawn was 2.3A. Switched on the Fan the voltage across the terminal was 14.25V and the current drawn was 2.7A. Switched on the AC and now the voltage across the terminal was fluctuating between 14.1V to 14.2V and the current drawn was 3.1A. Swiched on the lights with the AC ON (Full Load) and the voltage across the terminals was fluctuating between 13.6V to 14.1V and the current drawn was 4.2A. Then switched off the car. The voltage across the terminal was 12.8V. Started with the bulb series test. Disconnected the battery, connected a 12V bulb in series with the Battery and found bulb glow dim. After 30 sec there was a click sound in relay and the bulb stopped glowing. Left this in this series setuop for 10 min and not once did the bulb come on. Everytime I broke the circuit and reconnected there was a click sound and the bulb would glow dim and after 30 sec the bulb would switch off. What else test can I now do to find a drain.

Tiny
Agnelocorrea
Jul 1, 2012.
A computer is drawing heavy current in an attempt to go to "sleep mode". Current flow through the light bulb results in a voltage drop so the computer is actually getting much less than 12 volts. That equates with power being switched off, the computer turns off, current flow stops, no voltage is dropped across the bulb so supply voltage to the computer goes back up, the computer wakes up and prepares to go to sleep mode which can take up to 20 minutes, draws high current, and the process starts all over.

A bulb is not accurate for this test. They worked well many years ago when cars didn't have computers. A drain was typically caused by a trunk or glove box light not turning off. Those were significant drains that killed a battery overnight, and the test bulb would glow about half brightness.

With all the computers on cars today, it is common to have a drain that will kill the battery in a few days but is way too small to make the bulb glow. You need a digital amp meter instead but using that has its own problems from the computers timing out and going to sleep mode. Check out this page for a better explanation:

http://randysrepairshop.net/testing-for-battery-drain.html

You can have a car with no battery drain problem and the test bulb will act exactly the same as what you're seeing, or you can have a drain that is too small to show up with a bulb.

In your third reply, I assume the engine is running to get over 13 and 14 volts, so any current measurements are meaningless. There will be current flowing into the battery to recharge it but that should be closer to 5 - 15 amps. With all the things you turned on, current should be up to 20 - 30 amps but that would be coming from the generator, not the battery. Since the voltage dropped very little with those things turned on, that just means the generator is not having a hard time keeping up with demand.

Caradiodoc
Jul 1, 2012.
I have had a similar problem with my 2000 is200. We bought a newer car and have kept it as a second car and it has had little use since. I put the flat battery down its infrequent use.
But after many recharges and a couple of batteries I decided to look into why the battery was draining after only a week or so.

There is an additional siren in the boot/trunk that is there as a back up to the main alarm, incase the battery terminals are lifted to prevent the horns going off.

What I have deduced is the siren has an independent battery that had failed and when the car wasn't running the siren was dragging the main battery charge down as it was trying to keep the faulty battery healthy.
I removed the siren 4 days ago and the battery voltage is still healthy, down to 12.57v from 12.79v 4 days ago. There is still a little drain somewhere but it is a hell of a lot better than before.

The additional siren is easy to remove.
First remove all the junk in your boot/trunk.
Pull out the plastic studs retaining the boot/trunk lining on the drivers side, around the wheel arch.
Pull the lining away from the wheel arch and you will see 2 studs being held on by 2 10mm nuts.
They will be tight so you really need a 10mm spanner or socket to remove nuts.
Siren will be free to unplug and chuck away.

Hope this helps.

Tiny
Mar10b
Jul 10, 2012.
Thanks for the info. You would think this would a common enough problem that the dealer's mechanics would be aware of it and not have to waste so much time diagnosing the drain.

Caradiodoc
Jul 10, 2012.

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