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Battery draining

I have an issue with one of r cars where the battery is draining if it sits for a day or two. It is a new battery but had it and the alternator tested and both r good. The other day I noticed when the car is not on a clicking sound from the radio every few seconds. Is it safe to assume that the radio is what is draining the battery? We had a cassette get stuck and would not eject so we had to pry it out with a screwdriver.



You could pull the fuse for the radio and see if that prevents the issue.


Good idea above. A shop can do a phantom drain test to see what the problem is also. They install a current meter in the battery negative line and monitor it as they pull fuses to determine which circuit is causing the problem, then they narrow down what device it is on that circuit in the same way. Before doing all that, make sure all the lights are turning off when you turn the engine off and exit the door. Battery drain problems are often caused b/c the glove compartment light, engine compartment light, trunk light etc doesn’t turn off.

We have a problem that I hope you can help us with. In July we bought a 2018 Lexus RX 350. We only looked at Lexus because they have an excellent safety record and we have had great luck with a previous RX and multiple Camrys. We are retired and drive around 500 miles per month. The first month we had the car it refused to start on five separate occasions. The car was towed to Lexus and we were told the battery had discharged. The “company line” is that you need to drive the car a minimum of 1,000 per month for the battery to maintain a full charge. Lexus said the new cars have multiple computers that communicate even though the car is off. That was never explained to us when we purchased the car or is it indicated in any of the manuals. We contacted Lexus and they have agreed to install a battery tender permanently on the car and we need to plug the unit in to maintain a full charge. This seems like a poor solution considering we paid over $50,000 for the car. We have also read on the internet that other Lexus owners have had a similar problem.
Have you encountered this problem before and are there other more permanent solutions to the problem that don’t require plugging something in? Any suggestions you can provide would be greatly appreciated.
Very frustrated Lexus owners,
Courtney and Fred

Hmmm r=“our” and r also equals “are”. I guess doesn’t matter much here but if you ever sign a contract, make sure all the words are spelled out clearly.

Agree though, if you think it’s the radio, just pull the fuse for it and see if the drain goes away.

If this thing has the start/stop feature just get in the habit of turning it off every time you start the vehicle. Also you are retired why can’t you just take a relaxing drive of about an hour each month.

There are so many interconnected circuits these days that a schematic might be needed to shut down all the power to a sound system. There must be a dozen wires besides those to the speakers on late model cars and many are power sources.

All modern cars use computers. I think your dealer was extremely nice in installing an onboard battery tender.

That is total BS. Half the drivers in this country drive less than that. I’ve driven less than that for the last 20 years and two cars. They are just trying to get out of fixing your problem.

All the computers go to sleep after a short time and the total drain is usually less than 50 mA, low enough that the battery would last for months with no problem.

Try another dealer.

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Partially agree, chances are they are driving very short distances at low speed and not getting the battery fully recharged. I still think their dealer giving them an onboard battery tender was a perfect solution.

I’d be surprised if 500 miles per month isn’t enough to keep a new battery fully charged. When it didn’t start, do you mean it wouldn’t crank, that rr rrr rrr sound? Assuming so, there is probably something remaining turned on overnight & draining the battery. Ask the shop to keep the car several days and monitor the phantom drain current on the battery as it sits. It shouldn’t go above 50-100 mA once the car has been turned off and parked for 30 minutes.

If it goes above 100 mA then there is some circuit that causing the drain. With newer cars what can happen is a device fails (it could be the radio or the gps or the alarm system for example) and that confuses the computer system and causes it to remain on even after the car is parked. The drain test above will identify if that’s what is happening.

Also measure exactly how much you are driving. You may think you are doing 500 a month, but really only doing 150, and that could be contributing to the problem. 150 miles a month might not be enough to keep the battery charged on newer cars. In which case the battery tender is the only option, other than buying an older used car.