Heads up: Replace Key Fob Battery

Cosmacelf · Jul 2, 2015

So I recently got a warning on the dash that my key fob battery needed replacing. No problem, I have a bunch of 2032 batteries in the garage. I put a fresh one in, and check the car, warning message still there. Hmmm. Maybe that battery was old. Try another one. Same thing. Ok, maybe I need to drive it for a while to reset the system. Nope.

Long story short, it turns out that it was the other fob hanging in the hallway that needed a new battery, not the fob I carry with me all the time. The "I need a new battery" message from the fob seems to travel pretty far...

Chipper · Jul 3, 2015

Cosmacelf said:
So I recently got a warning on the dash that my key fob battery needed replacing. No problem, I have a bunch of 2032 batteries in the garage. I put a fresh one in, and check the car, warning message still there. Hmmm. Maybe that battery was old. Try another one. Same thing. Ok, maybe I need to drive it for a while to reset the system. Nope.

Long story short, it turns out that it was the other fob hanging in the hallway that needed a new battery, not the fob I carry with me all the time. The "I need a new battery" message from the fob seems to travel pretty far...

I am surprised there is a message at all. I have had my P85 for 18 months and my battery went completely dead last summer. I got zero notifications. I wonder when they added this notification?? I LOVE the fact that our cars just keep getting better!

scottm · Jul 3, 2015

So is it better to store the fobs far away from the car, out of pinging range, to prolong battery life?

Currently thats what Im doing. The spare is a couple of rooms away from the garage, not in the back hall next to the garage door where all the other keys hang.

arg · Jul 3, 2015

Cosmacelf said:
Long story short, it turns out that it was the other fob hanging in the hallway that needed a new battery, not the fob I carry with me all the time. The "I need a new battery" message from the fob seems to travel pretty far...

That's almost certainly why the battery needed replacing in the first place!

The fobs work by the car continually transmitting on one frequency; the fobs are normally dozing in a low-power state but wake up when they hear the beacon from the car and then transmit a reply. So a fob that's within reach of the car's transmissions will use up the battery much faster than if they are dozing in a radio quiet zone.

Also potentially an issue with the car failing to lock if you rely on walk-away locking and the car parked close to the house.

jerry33 · Jul 3, 2015

scottm said:
So is it better to store the fobs far away from the car, out of pinging range, to prolong battery life?

Yes. in other cars 5 metres is the recommended distance. I doubt it would be different in the Model S. (I don't recall any distance being specified in the manual, but I could have missed it.)

manis · Jul 3, 2015

scottm said:
So is it better to store the fobs far away from the car, out of pinging range, to prolong battery life?

Currently thats what Im doing. The spare is a couple of rooms away from the garage, not in the back hall next to the garage door where all the other keys hang.

Unless a significant other is going to use the spare might as well just take the battery out and put a rubber band around them or something. That's my plan once I pick up my car. Seems like the spare is going to die during the same period as the primary one, at least this way you might have a good battery handy if you don't have a battery laying around.

jerry33 · Jul 3, 2015

manis said:
Unless a significant other is going to use the spare might as well just take the battery out and put a rubber band around them or something. That's my plan once I pick up my car. Seems like the spare is going to die during the same period as the primary one, at least this way you might have a good battery handy if you don't have a battery laying around.

If it's not within pinging distance, in or out won't make a material difference in life.

manis · Jul 3, 2015

jerry33 said:
If it's not within pinging distance, in or out won't make a material difference in life.

But it has to trickle enough power to ping or be pinged (not sure if it does the pinging or the car does)

jerry33 · Jul 3, 2015

manis said:
But it has to trickle enough power to ping or be pinged (not sure if it does the pinging or the car does)

The car does the pinging. In the Prius, which works similarly, the battery in the spare fob lasts for years (at least five). That's why I said "material difference".

Cosmacelf · Jul 3, 2015

The funny thing is that while my spare fob seemed to be close enough to occasionally tell the car that it is low on battery, it isn't close enough to allow the car doors to open. I had to be close the car with my other fob for the doors to open (I have auto lock).

caddieo · Jul 3, 2015

scottm said:
So is it better to store the fobs far away from the car, out of pinging range, to prolong battery life?

Currently thats what Im doing. The spare is a couple of rooms away from the garage, not in the back hall next to the garage door where all the other keys hang.

Yes. Distance is important and there have been various posts as to how far. In addition, some RF shielding is advisable. I keep mine in metal containers in the foyer leading to the garage. It's easy for me to do as my fobs are used by themselves and not attached to key rings or whatever. I also recall some posts that recommended putting the fobs in the refrigerator. How's that for shielding? :wink:

jerry33 · Jul 3, 2015

caddieo said:
I also recall some posts that recommended putting the fobs in the refrigerator. How's that for shielding? :wink:

Should be good as it's mostly surrounded by metal.

TexasEV · Jul 3, 2015

Chipper said:
I am surprised there is a message at all. I have had my P85 for 18 months and my battery went completely dead last summer. I got zero notifications. I wonder when they added this notification?? I LOVE the fact that our cars just keep getting better!

Didn't they replace the batteries in your key fobs at your annual service? That's on the list, but you have to remember to give them your spare key fob.

jerry33 · Jul 3, 2015

TexasEV said:
but you have to remember to give them your spare key fob.

That's the hard part

GaryREM · Jul 3, 2015

TexasEV said:
Didn't they replace the batteries in your key fobs at your annual service? That's on the list, but you have to remember to give them your spare key fob.

The SC gave me a spare battery for the other fob at my annual service.

caddieo · Jul 4, 2015

GaryREM said:
The SC gave me a spare battery for the other fob at my annual service.

I got one also.

mikeg561 · Jul 4, 2015

I store my car keys kind of close to the car, so I wrapped my spare fob in aluminum foil. Before the foil I could lock/unlock the car from the key drawer area. After the aluminum foil, I could not lock/unlock. I am going to assume that means the car can no longer ping the fob.

Mike

rickgt · Jul 4, 2015

let us know if this works... my spare is about 25' from the car.... might be a problem.

mikeg561 said:
I store my car keys kind of close to the car, so I wrapped my spare fob in aluminum foil. Before the foil I could lock/unlock the car from the key drawer area. After the aluminum foil, I could not lock/unlock. I am going to assume that means the car can no longer ping the fob.

Mike

mikeg561 · Jul 4, 2015

It works. Like I said, without the aluminum I could lock or unlock the doors. With the aluminum, I can not. I don't think there is any way to tell if the car has pinged the fob. Is there?

rickgt said:
let us know if this works... my spare is about 25' from the car.... might be a problem.

GlmnAlyAirCar · Aug 12, 2015

Hmmm, I thought I was storing my key far enough from the car (approx. 17 ft.) but my fob went nearly dead (no auto-unlock, need repeated presses of unlock to make it happen) yesterday, just 10 weeks after getting the car new. The spare (kept further away in a fireproof safe) is fine. That seems pretty quick for the battery to die, even if kept within pinging range.

Should I get the $1.99 battery on Amazon or the $600 battery at my first service? :wink:

Heads up: Replace Key Fob Battery

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