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Lexus RX350 Battery Drain Problems

My Mom purchased a new 2011 Lexus RX350 last spring. The dealer installed a remote starter at the time of purchase (we live in Alaska). We’ve had a continuing problem with the battery going dead if the car has not been driven for a period of time (like 4 days). When she does drive it, it is for short trips (3 miles round trip to work). The original battery was replaced in fall with a heavy duty one, but the problem continues. Its been to the Lexas dealer (130 miles away) several times, but they claim everything is within the tolences and “there is no problem”. They did note that the remote starter was drawing more than it was suppose to and reinstalled it. Their finding was that she was not driving it enough and recommened a battery tender, which has been installed. That works as long as she plugs it in daily. However, if a plug in is not available (like at the airport, hospital or if she is visiting) the battery goes dead after 4 days (even after it has been driven 100 miles).

This does not sound right to us, but the Lexus service department has no clue and claims there is nothing in the service bulletins about this problem.

We don’t beleive this is what to expect from Lexus. We are about ready to give it back and get a different brand. Any idea’s?

Are you sure the trunk light is off?

Something must be drawing power with the ignition switch off. If you know how to use a current meter* , you can probably figure out where that current is going.
Set the meter to read current in the order of 200mA. With the ignition key off and the doors closed, pull out each fuse and put the meter across what that fuse plugs into. You shouldn’t see any appreciable current flowing.
If one does flow a lot more than any other, that’s likely the curprid. Whatever that fuse protects is drawing more current than it should. See what happens after four days with that fuse out. If you can start the car, there’s something that needs to be checked.

(*a multimeter like this has that function:

This is a good approach but the drain for a 4 day depletion is a bit higher. In alaska it depends on the temperature and I hope the dealer is using battery capacity properly rated for the lower temp range. Many retrofit devices are not properly installed and that is what I worry about. Plus the dealer is not what we call in the lower states LOCAL. If they placed a fuse for the remote start I would just pull that for a few days and see what happens.

You can’t pull a fuse on todays cars and check for a current draw. When doing that you can force a computer/module to go to sleep that may be drawing the current and never find the current draw.

Instead, leave everything connected and take an infra-red thermal gun and point it at the fuses and relays. If you find a fuse/relay that’s hotter than the others, that circuit is drawing higher current than the others and should be investigated first.


Almost right. You really cannot see parasitic drain on any infra-red I have used. The heat just dissipates over the copper and the differential is pretty small. I know there are better ones for more money than a person would want to spend. There are fuses perfectly ok to remove without your concerns about clocks and ecu’s however. This technique is still valid and you should know this. That said this drain is either larger or the battery less able to provide a larger amp drain.

It would depend on the resolution of your thermal gun. I have both high/low resolution thermal guns.

But there’s another way to check for a current draw without pulling fuses. Take a volt meter and measure the voltage drop across the fuses. A fuse with a high voltage drop means the fuse element is hotter than the others which means that’s the circuit drawing the current.


I was assuming a test at the fuse. I did not make this clear. An amp drain test by pulling the fuse and then testing across the fuse contacts. Not the battery terminals. I should have been clearer.

What would help is to know how many milliamps are being pulled; both sans remote starter and with remote in place. One would hope the dealer would have checked this and properly done it should have been put down in writing on the repair order.

You’re not getting it. What if there’s a module that isn’t going to sleep. If you disconnect the battery or pull a fuse that forces that defective module to go to sleep. And then if you check for a current draw it won’t be there. Because you forced the module causing the problem to go to sleep.


Module draw is live when it is told to be live. Otherwise our cars would never start. If it is not going to sleep, a rare issue, then you can also pick this up. A thermo scan will not see an active drain easily on a 600ma drain across a 20 amp plastic encased fuse either. But given the mods to this car I would start there and I am sorry if you disagree.

Here’s the first procedure when checking for a parastic current draw on a modern vehicle. Let the vehicle sit for at least an hour to make sure all computers/modules have gone to sleep.


Fine, Just trying to give ideas to an OP who has to burn 260Miles of gas in alaska (higher than 4$ a gallon I bet) to get back to the DEALER, who likely caused the issue to begin with. You are right up to a point but then I have nothing more to say as it will not change anything.

Not for nothing but could one see power dissipation across a fuse with a thermal scanner if the current is just - say - 40 mA?

I’m assuming some normal batter so somewhere around 40 AH and let’s assume that drains over four days to being dead as a door nail. That’s 40/4 = 10AH per one day. That’s 10/24 = 42 mA.
LEt’s assume the fuse is a horrible fuse and has an internal resistance of 0.1 Ohm.
That means that the actual power dissipation of that fuse is 0.42 * 0.42 *0.1 = 0.2 mW and I’m being generous with the numbers, rounding them before calculating.

You can’t see 0.2mW on a wire.
There won’t be any appreciable amount of heat dissipated by the wire. The fuse is in an outside area (in cold Alaska no less!) and it wants to be at ambient temperature.
You’d have to drain a lot more current than just 40mA. If the dealer can’t find where some parasitic drain is going, they have no business repairing cars, let alone putting remote starters on.

There’s no way that car shouldn’t last for weeks if left alone. Sure, Alaska is cold but your summer is probably still warmer than our CT winters. We leave our cars in long term parking all the time at the airport for weeks on end without any issues.

I agree with the other suggestion of disconnecting the remote start fuse first. Actually bring it to the dealer and make some noise. They clearly are morons.


Thanks for all the comments. The RX 350 is an SUV, so it has a hatch not a trunk. Checking for the light has been easy, and that has not been the issue.

The car lives in a heated garage most of the time and that is usually where it had the dead battery until we got the trickle charger.

We’ve read some posts on the “Club Lexus” web site that suggests disabling the “Smart Key” when the car is not going to be used for a long period of time (like when she is out of town for a week or longer). It appears this has happened with other Lexus models (also BMW’s and other electronically tripped out cars from what we have seen on the discussion boards). However, her manual does not discuss this or the location of the switch. Any thoughts?

And yes, gas is $4.47/gallon in her home town, $4.20 in Anchorage currently.

Tiny levels, though.
4.5mV on single ended wire into a high impedance (ie open wire because the circuit is off) could easily be construed as noise. A regular half way decent multimeter measures about that much if you just leave the leads dangle.

Also, if specialized equipment is involved it no longer is a home mechanic approach.

It would be nice to know how bad the current drain is on this. The Lexus shop should be able to fix this problem. There are other shops in Anchorage that could look at the issue also. I live in Anchorage and if you would like me to check it out let me know.

I agree with Cougar that it would be nice to know what kind (amount) of parasitic loss is involved.

While I’m not familiar with the vehicle in question as to what’s normal or not I might add this in relation to what Tester stated. Both of my Lincolns and my youngest son’s Lincoln Aviator have comparatively large parasitic drains until things settle down and go to sleep. We’re talking 700 milliamperes for about an hour and that type of draw can run down an iffy battery in that length of time.
Assuming a new battery for the sake of discussion, a draw that large can run a new battery down if things don’t go to sleep pretty quickly.

Maybe this large draw the dealer referred to was an initial current draw without waiting for things to go to sleep. I also don’t see a mechanic driving a car into the shop and allowing it to tie up rack space for an hour while waiting for it to doze off… :frowning:

On a side note, if this remote unit was not installed in the service department and was done by an outside vendor then one runs into the sticky issue of exactly who is going to pay the mechanic for sorting this out.
Warranty will not cover it, the dealer will not cover it out of pocket, etc. and a mechanic who is coerced into doing something for free is not going to give a darn.

Wow, OK4450. I am surprised to hear that high of current numbers for that long of time period.

The OP said “The dealer installed a remote starter at the time of purchase (we live in Alaska).” I just wanted to say.