About 2 weeks ago the battery went flat in the '06 RL. I thought ti was the battery as it was about 5 years old. It was weak but not dead when it was tested. So, given the age I installed a new battery. Today the battery was flat. So I charged it. I put the light bulb test to the positive terminal and it glowed bright, evidently there is a big draw on the system.

The car starts, runs, drive normally with no code lights. All of the electrical works. I even checked the trunk light to make sure it wasn't on by going through the back seat hohle to check it. Nothing I can find is ON.
I came in here and started to research it. Nothing definitive came up.

The next step was to check all the fuses in the box under the hood...all OK

Then I started pulling fuses behind the driver's kick panel and testing with the light bulb.
Fuse #5 the light went out when the fuse was pulled.
The fuse is for the RADIO. What could the draw on the battery be from the radio?

I am requesting your help.

 

The bluetooth handsfree and the door handles are both known issues for phantom current draw - check those first. You can solve the handsfree issue by simply disconnecting it - I'm guessing it's fused along with the radio as part of the system, but I don't know if this is correct...

 

UPDATE: I swear I am going crazy. I watched a video on how to check for a drain on the battery using my multimeter. I am getting no draw. After pulling fuse number 5 and resetting the radio/navigation unit codes, there doesn't seem to be any draw. I thought I was doing something wrong but after re-watching the video, I am doing everything as it shows.
I might go back to the light bulb test.
Last night the battery was at 12.78 volts and at noon it was still at 12.78 volts.
I am going to be watching this over the next few days looking for a voltage drop.

I find this to be some really strange behavior.

 

As they say in IT: have you tried turning it off & on again?

I believe you just did...

 

The radio is controlled by the key, so why would it matter if it is turned on or off? Using the light as I previously mentioned between the positive post and the cable, the light went out when I pulled fuse #5.
I did notice that the drivers seat heater was turned on, but then again that should be key controlled.
Never the less, the issue has resolved itself...at least for now.

 

I agree its controlled by the key, adding that any modern radio has a memory function that is always on as well as multiple modules that "wake" when the door opened and when you approach the car with the key.

To the point above there are known issues where the modules do not time out and will draw the battery down, in this case by resetting the car you resolved the issue.

 

I downloaded the wiring diagram for the RL and found out that fuse #5 is hot all the time. It feeds the radio and the interior lights.
I pulled the fuse and the drain on the battery appears to be gone.
The interior lights seem to me to be where the issue lies. Now to find out what lights are on. At this point I haven't seen any that are on. The best way will be to be in the car when the interior lights go out in a dark garage.
More information as it comes.

 

Update: The battery would be fully charged so I made a run to the store and I almost didn't get the car restarted. With the help of a neighbor, we tested the alternator and it was putting out 14V+ so that wasn't it. We put a load tester on the battery and it went to *bad*. The battery is only 3 months old and would charge up but when a load was on it, it tested bad. So, there was a bad cell in the *new* battery. I took it back to the store and they gave me a new one. So far so good, but as it is said, time will tell.

 

I’m running into something similar and I’m curious where yours ended up. I had a five year old battery that went dead a month ago. I had O’Reilly’s test it and they said it was bad. I believed them enough considering it was near the estimated lifespan.

I replaced that a month ago and my new battery was dead this morning. I can’t see any lights on and my battery tester says it’s healthy. I’m watching the voltage while it sits and it’s a little confusing. After driving for 20 minutes, earlier today it dropped from 12.4v to about 12v while I had lunch.

I drove for another hour and a half this evening and it seems to be holding a charge around 12.9v.

a friend had a clamp meter and we couldn’t obviously see a big draw. Pretty confused.

from reading this report, I wasn’t clear if you did anything other than unintentionally reseting the system due to a dead battery.

anyway, pretty confused and curious if you found anything. Thanks!