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.




Here's a copy of a reply I posted previously: Testing for a drain can be a little tricky with all the computers on the car. Some of them can draw a high current for up to 20 minutes until they go to "sleep" mode. Anything you do to momentarily break the circuit starts that 20 minute wait period all over. That includes switching the range on your ammeter. If you start out on a higher scale you won't get the necessary accuracy. If you start out on a lower scale you can pop the meter's internal fuse. On top of that, some computers can lock up after the battery is reconnected but that doesn't seem to be a big problem yet in 2003 except on Volkswagens.

The secret is to disconnect one battery cable to insert your ammeter AND connect a jumper wire across the meter to in effect short it out. Some computers might "wake up" so let the meter and jumper sit there for at least 20 minutes, then remove the jumper wire. All current will go through the ammeter so it can be measured. If you need to switch to a lower scale, put the jumper wire back in place first, switch the meter, then remove the jumper again.

Unless the manufacturer specifies differently, the industry-accepted maximum is 35 milliamps to maintain the memory circuits in the radio and computers. At that rate a good battery will still start the engine after sitting for three weeks. Slightly more than that won't kill the battery overnight but you don't want to see 200 milliamps or more.

Typically when there is a drain, it's really a drain. You won't have to guess. You'll likely find an amp or more, especially if the battery goes dead overnight. Remove one fuse at a time to see if one makes the current drop to an acceptable level. That fuse's function will give you an idea of which component to look at.

Caradiodoc
Apr 14, 2012.
Once the main fuse is removed, shouldn't the power to all electricals be cut. Of all the electricals are cut then there shouldn't be any drain. But I still find a drain inspite of the fuse been removed. Also can you let me know if the alternator can drain the battery when the car is not started with all electricals disconnected.

Tiny
Agnelocorrea
Apr 15, 2012.
First be sure the top of the battery is clean. If condensed acid covers it, the battery will self-discharge through that acid. That acid is caused by excessive bubbling in the battery which is about to fail in the next few months.

The voltage regulator is built into the generator. The circuitry in it could cause the battery to discharge but that would be very uncommon. There are also two sets of diodes which are one-way valves for electricity. One diode in each set would have to short to drain the battery but that would be a serious short that would blow the fuse or melt wires. That would also kill all output from the generator.

To see if the regulator is the problem, unplug the connector next to the bolted-on output wire. If that stops the discharge replace the generator or its internal voltage regulator.
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Caradiodoc
Apr 15, 2012.
I did a series of check. Alternator Output when car is Idle - 14.04 - 14.1 Volts. When the car is at 1200rpm - Alternator output > 14.1 Volts. The current the battery is drawing is approx 15 - 17 Amp when the car in on. The drain current when everything is shut down is 20 - 30 mA. Still I find my battery drain. The battery is charged to 12.3 volts as I have a volt meter in the car. After 1 - 2 hrs I find the output voltage to be below 11.5 volts and gratually drains to 8 volts and then finally the battery is flat. Is there anything else I need to check. I have checked the cig lighter for any peices. Also I have checked the battery leads and have cleaned the leads to remove any acid residue but there wantn't any. Please guide.

Tiny
Agnelocorrea
Apr 15, 2012.
35 ma or less is perfectly acceptable. At that rate, a good battery will still start the engine after three weeks. I would suspect the battery is getting old and its capacity has gone down due to the normal lead flaking off the plates. It should be maintaining 12.6 volts when it's fully charged.

There likely are computers on your car that go to "sleep mode" after the ignition switch is turned off. When the voltage from a weak battery drops enough over time, it is possible for those computers to "wake up" and draw heavy current which isn't showing up in your current drain measurements. I'd try a new battery first.

Caradiodoc
Apr 15, 2012.
Thank you very much for your help. This is my third battery in the last 3 months. The 1st two bateries were from Halfords. The first battery was 490Amps while the second was 510 Amp. I faced problems with both of them and finally took it to Lexus to get the issue fixed. They concluded that there was no drain and the battery was weak for such a heavy car. They advised me to replace the battery to 570Amp which I did and this battery is from Lexus and fitted at Lexus. Would you think that I am the unfortunate one to get 3 batteries bad in a row. I highlighted this problem to Lexus and they did all the checks to tell me that there is no drain and they have never faced a problem like this before. Pls help.

Tiny
Agnelocorrea
Apr 15, 2012.
The cold cranking amps isn't really a big factor here. The typical starter today only draws around 150 amps so a battery with lower cold cranking amps will get the job done. More current is needed when the engine is real cold, and batteries lose some of their capacity when they're cold but their CCA rating is for when they're cold. Their capacity goes up in warmer weather. To be safe, your battery needs to have twice the CCA rating as your starter draws. You have well over three times the capacity so that is not an issue.

Even a battery with a high CCA rating might only be able to deliver that current for a short period of time. Many batteries with lower ratings can deliver their maximum current for longer periods. Your batteries all meet the needs of the starter and since they were new, there should have been no problem holding a charge for three weeks.

My best guess is something is turning on after the engine has been off for a while. That is one of the drawbacks of all the computers used on cars today. I've run into a radio amplifier that turned itself on after a few hours. That was found by the owner who noticed a slight hiss in the speakers that wasn't normal. I also had corrosion between two adjacent terminals in a Body Computer connector. One wire was hot all the time to park the windshield wipers even if the ignition switch was already off, and the next wire was for the parking lights. When humidity went up in the car, presumably when the fresh air stopped flowing from the heater, the corrosion conducted enough current through the tail lights to drain the battery in a few days. I found that one by accident after removing the connector and seeing the corrosion. I also have a '72 Challenger in which the factory radio would suddenly start playing a few hours after the ignition switch was turned off. Turning the switch on and back off stopped the radio for another few hours, then it turned on again. That turned out to be two overheated wires in the firewall connector that were melted and barely touching. A little current flow would warm the wires enough to expand and touch sending current from the battery circuit to the accessory circuit off the ignition switch. The radio would get enough current to start playing but it would turn off if I turned on the wipers. Not enough current could get through to run the wiper motor so the voltage would drop enough to stop the radio from playing. Simply bending those two wires away from each other solved that problem. Now imagine what can happen when you add a whole lot more computers and other electronics to a car.

This type of electrical problem can be real frustrating to find, especially if it doesn't act up all the time. Since you have a new battery already, the next thing I would suggest is using an auto-ranging digital meter to monitor the current drain over a few days. Check on it every half hour to see if the current suddenly increases.

You might also have your new battery load-tested again, but also have the generator load-tested with a tester that measures "ripple". Ripple is not displayed as a voltage; it is displayed as a bar chart from low to high. If ripple is high, suspect a defective diode in the generator. It will also only produce exactly one third of its rated capacity. That will take a real long time to fully charge the battery because one third of normal capacity is barely enough to run the electric fuel pump, ignition and fuel injection systems, radio, and a few lights with little left over to recharge the battery. That COULD explain why your battery only has 12.3 volts instead of 12.6 volts.

Caradiodoc
Apr 15, 2012.
Thank you once again. I am taking the car to Lexus tomorrow for a check again. The latest I could find is that the battery is 570Amps but with the battery tester it shows 47Amps. I am not sure if this is cause there is no sufficient charge in the battery as it has drained and I have to drive it for a couple of hrs to recharge the battery to its maximum.

Tiny
Agnelocorrea
Apr 15, 2012.
Also just to correct the readings once the car is on the battery charges to 12.7 volts and as soon as the car is switched off the charge starts falling down.

Tiny
Agnelocorrea
Apr 15, 2012.
If I understand correctly, the engine is running when you measure 12.7 volts at the battery? That's way too low. It must be between 13.75 and 14.75 volts.

12.7 is fine after the engine is stopped.

Caradiodoc
Apr 15, 2012.

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