electrical battery drain

Bret - I have the same problem with my lexus and followed your advise. I inserted an ammeter and came to a steady-state reading of about 50 mA, which you say is where it should be. Nonetheless, the battery is always dead if I don't drive the car for a week or so. My mechanic says all electrical systems are okay. Do you have any other suggestions? Thanks for your help.

First and foremost, verify that your Alternator is charging at a level of at LEAST 14.2 volts at idle. Then verify that the diodes in the alternator are good with a diode test. You first have to have a stout charging system before you tackle a parasitic drain. Then, with a volt-ohm-milli-amp meter, connect the meter in between the negative post and negative terminal of the battery and have it on the 10 amp scale. wait at least 30-45 seconds to let the computers go to sleep. This is with the key out, all lights off and all doors closed. The amp reading should go down to about 50 miilamps or less. If it is reading 250 miilamps or more, then you definitely have a drain. Then remove 1 fuse at a time and, starting with the under hood fuse panel and keep going until you find the circuit that is draining the battery. When you remove the correct fuse, the amp reading will drop down to the 50 or so milliamp target. If you are still lost, contact Bret at RepairPal and ask for me. I work in San Bruno and have skills at Electrical Drain Diagnosis, I will try to help you. Dear JP, A 5 watt resistor is way to sensitive. The stop light circuit is 'hot' all the times as a safety feature. So, if you have an excess of current, then first use a test light. That will light and will not blow or get too hot. An milliamp meter is for very subtle stuff, not a fuse blowing situation. It sounds like you have a short that is bad enough to blow the fuse, intermittently. (Coincidentally, I am tracing an intermittently fuse blowing short on a Nissan Altima, the power wire will start smoking before the fuse blows, 10 amps is a lot of current, think of 9 100 watt light bulbs in your home i.e. 110volts/100 watts = .9 amps because amps x volts = watts ) So, start disconnecting components in your stop light until the test light goes out. Don't rule out a defective lamp socket either. let me know if you need more assistance. Dan from RepairPal

Good information here, Dan lays it out exactly right. I'm glad he is willing to look at this, because the shops your going to seem to be incapable of handling this. If you need to contact us, go to our homepage and click the "feedback" link at the bottom of the page. On the "Feedback Category", select "Car Information Feedback" and reference this question and I'll get you in touch with Dan's shop.

BTW- The fuse which controls all the lights is call the 'DOME' fuse. I located it using the trial and error method. So not we know where the drain is coming from. Big woop because no one seems to know how to fix it.

1999 RX300 260,007 miles just last Jan 3 2015... ..Same scenario , HAD i KNOWN that bulb was the cause of my constant worry about my battery being discharged every night i would have saved myself buying the new battery, which also drained the next day.. i read in the blogs about burned out bulb issue from by bswtwa on April 03, 2013... AND BEHOLD. YES THE 3RD BRAKE LIGHT BULB WAS THE CULPRIT!!!!= a sylvannia $4.50 bulb that uses 12.8V caused my battery to drain each night. its baffling to me.. replaced it last night and hoped for the best .. now this morning , no more battery light warning. !!!!

@Froggy67, Thanks for the information about the third brake light, my Rx 300 is having the same issue when it seats 2 days straight with out moving, and surprisingly, there is a warning in the dashboard about a light. i am almost sure that could be the issue.

I had exactly the same issue-- 3 batteries, replaced the alternator, drains seemed to be about 50mA, which should have lasted a month, but each time, the battery would be dead in 3-5 days. A recent clue was that my external charger, which usually charges for a while, then goes into float mode, remained at .7A. WTF? On a wild hunch, I removed a dash cam that I had been using for months, and all my problems stopped. I think that the CMOS circuitry would frequently latch up and drain the battery-- perhaps when the super-cap in the dashcam would hold a charge, and the power lead would experience a momentary sharp drop, like when a pump motor came on or the trunk closer, and it would cause the latch-up problem. I struggled with this for months before finding it.