Don’t remember if it was the Lexus app or the car itself. How can I tell which of my 2 FOBs has a low battery?

 

If the fobs are the same age, just buy two new batteries and replace both. It is kind of like replacing tires in pairs.

 

Second this. The batteries are cheap and you save money buying in pairs anyway.

 

I bought in pairs, still get a message like this from time to time.. what might be the reason, anybody?

 

Those unused batteries have a long shelf life (years), so don't hesitate to buy them in packs of 4 or 6.
I only have one driver, so I put the unused fob into "sleep mode," (aka "battery saving mode") which results in no battery drain at all (the fobs are always looking around for a matching car). [Hold in the unlock button while pressing the lock button two times; the red light will flash 4 times. Press any key to activate again.]
A weak battery can sometimes be detected by a shorter effective range for the lock/unlock buttons; if you think only one is weak, try walking toward the car while pressing buttons on each fob. The first fob to make the car beep wins, and gets to keep its battery for a while longer. Change the other.

 

I change ours (all four) every Jan 1st. They'll actually last much longer than one year but with this method, I never have to think about it.

 

Yesterday, I received the same message: key fob battery low.

 

I have noted that the key fob battery condition is noted as "Good" in my Lexus phone app. But it does not say if that is for one particular fob or both of them.

 

If you leave your keys close enough to the car, it might be detecting it constantly, which could drain the battery.

 

Since it is the vehicle which assess the state of the key fob battery and reports it upstream to mothership Lexus as part of the vehicle's health status, it is most likely the last assessed key fob battery that gets reported in the Lexus app.

Considering that some ESs are delivered from the assembly line with 3 SmartAccess devices (2 fobs and 1 card) there's no consistent and reliable means of reporting the state of the battery installed in all the devices. Some of the fobs may have been put into battery saving mode or some of the devices may be out of range of the paired vehicle for extended periods of time thus leaving the battery state of those devices as unknown.

 

I have had the low keyfob battery warning for a month, I have put a spare battery in my wallet and will only swap it when keyfob is completely dead as it clearly still has some life in it.

 

you've got to be kidding.

 

In your wallet? Why not in the glove box, or in the console. or in the box on the left of the dash designed, I think, for parking meter quarters that nobody uses any more since parking meter apps took over the sidewalk. And "completely dead"? The effective range of the fob decreases as the battery dies out.
That seems like a lot of inconvenience to squeeze an extra 5% out of a battery that costs a dollar.
I just keep mine in a drawer in the house.

 

I keep the battery in my wallet as I also have the lexus key card fob in my wallet, so if I ever can't get into my car I can just swap in the spare battery in 2 sec, makes sense to me and saves me 25c or something :/

 

Thanks for the tip. Actually, it's -- Hold in the lock button while pressing the unlock button two times.