Leaving the fob in the car not only drains the fob battery, but it can also drain the car's 12 volt battery because, as long as the fob is in the car or even close to it, the fob and the car will be trying to communicate with each other constantly. That could well be why you needed to replace the fob battery after such a short period of time.

I'll guess that there is something in the manual warning you not to store the fob in the car.

 

Thank you very much. I ‘ve learned something important tonight. Will keep fob out of car and out of garage until I use it. Must not be quite the same though for our late model Audi and Volvo. No matter. You’ve solved my problem and I appreciate it.

 

Do your Audi and Volvo have keyless ignition/push button start? If they do, you would have battery drain if you stored their fobs in the car. On the other hand, if they have a traditional ignition that requires inserting a physical key into the ignition, storing their fobs in the car would not cause a problem because their keys/fobs are not constantly communication with the car.

 

Beginning on page 92 of the 2021 manual, there is a lengthy discussion of the keys. It does state that the key will enter a low power mode if it is left too close to the vehicle for more than 10 minutes so that seems to contradict the low battery idea (assuming the electronic key is working correctly). It also has some information about the key touching metal objects that may interfere with communication. It also states that you shouldn't leave it on the dash and that coin tray could be considered part of the "dash"? Might be worth a scan to see if any of it applies to your situation. Could have just been some strange fluke as there isn't anything I can spot in the manual that identifies a clear smoking gun. I only did a quick scan however...

 

Perhaps a bad battery to begin with - NEW means Never Ever Worked!

 

I just read the very similar section of the manual for my RAV4. From my reading, I think there is a difference between the "low power mode" and the mode that disables the fob. I think that, in the low battery mode, there is still some battery power being used by the fob. Only disabling the fob eliminates any battery usage at all. I also noticed that at least one paragraph in that section applied only to hybrid vehicles, and I think that the OP has an ES350.

The thought that also crossed my mind is the manual would be more useful if it had been written by someone with a greater proficiency in using English than what appears to be the case.

 

Never really thought about this until I read this thread but in my manual it does state Do not attach metallic or magnetic
materials to the keys or place the keys
close to such materials. I have always had my metallic keys attached to the metal ring that came with the fob with no problems. If there statement is true why did they have a metal ring attached from factory. Do others have keys attached with no problems.

 

I've read the fob should not even be kept in the house, in a room close to the garage as it could deplete both the fob and car battery! Your car battery depletion is not an issue if you drive the car regularly.

That said, fob battery preservation, and the fob being able to communicate with the car are separate issues, but related. The fob battery will last longer if it is kept out-of-range of the vehicle's receiver/transmitter, when not in use (as I reported, my fob batteries last about five years). The other issue is to avoid shielding the fob's transmissions, as this will deplete the fob battery faster.

If one's fob is in one's pocket or purse, behind one's phone or keys, and the fob happened to have a weak battery, one may need to take it out and place it close to the start button, but, maybe not, if the fob battery isn't low.

Sorry if I'm over-explaining this!

 

Just store the fobs in a Faraday pouch when at home.

 

Ironically, my dealer includes a very nice "Lexus" branded metal keyring/ornament with the name and number of the dealer on the back. Another contradiction? Perhaps they learned from that experience because they provided a leather version with the recent RX purchase.

 

They’re both late model cars with push button start and smart keys. I do find myself changing their fob batteries every 18 mos. or so. They’re stored from Dec through May when we’re away from home in Florida. Then the key fobs are removed from car and garage. So it all adds up. Lexus fob now removed from car and garage when car not in use. Problem solved.

 

Both my wife and I have keys attached to the fob - no problem whatsoever.

 

I suspect that it would take a large amount of metal to interfere with the operation of the fob. While I've never attached anything at all to the fobs for cars with keyless push button start that I've owned, I've always kept the fob in one of my pockets, and it is the same pocket where I keep my keys. I've never had a problem with doing that, and my fob batteries have typically lasted for 4+ years.

 

Wow - I change them every year - never tested to see how long they actually last but I figured a year might be overkill.

 

If I remember correctly, I think that the manual for my RAV4 Hybrid says that fob batteries for cars with the keyless fobs/push button start should last for 1 to 1 1/2 years, and fob batteries for cars without push button start should last 1 1/2 to 2 years, but the fobs for my 2013 ES (with push button start) still had their original batteries when I traded the car 3 1/2 years after I got it. I sold my 2017 ES after 4 1/2 years of ownership, and I replaced its fob battery one time about a month or two before I sold it. I owned a 2005 GX (without push button start) for 15+ years. I changed its fob batteries only 2 times during that period of ownership.