fob battery and 12v battery

One data point: After 3 years my 12v battery needed replacing, but both SKS fobs are fine so far...

 

The FOB battery should go 7-10 years. In my experience, FOBs wear out from pocket abuse before the battery dies.

The 12 V battery life is dependent on whether it has been accidentally discharged. If it has never had this happen, it should last 5 years. If it's happened once, I'd estimate 3 years life. Less if it's happened more.

 

The fob battery life can be shortened if you keep it near a cell phone, such as in the same pocket. The RF from the cell phone can spoof the fob into responding repeatedly, which greatly shortens the battery life.

Tom

 

Another car, another fob, but perhaps the story may be of interest.

I own a 2002 Audi A4, and always use the fob to lock and unlock the doors.

About a year ago, I started noticing that occasionally I would get a specific beep pattern from a source hidden behind the rear seat just after starting the car. Always the same: I think it was about five beeps, about ten seconds after ignition.

This summer I decided to check that I could figure out how to replace the fob battery (the owner's manual sends you to the dealer). Checking the voltage, I found it considerably down, so replaced it from stock in hand.

A month or so later I realized I had not heard the post-ignition mystery beeps in quite a while--and I still have not. I surmise that somehow a low fob battery in that car could have that undesirable effect.

I'd not like to get caught on a cold day with a malfunctioning fob, so if I remember, I intend to replace our Prius fob batteries after no more than 5 years, even if I have not noticed anything. Lithium cells fall off a cliff once they finally are near the end, much more rapidly than most other consumer battery chemistries.

Back to the Prius. Can anyone post specific symptoms they have observed for a near end of life fob battery in the Prius?

 

2005 Prius (purchased April 2005, about 60k miles). I had to replace the 12 V battery a couple of months ago, so 3.5 years. The fob still works, but i occasionally need to pull it out of my pocket and press the buttons on the fob to lock or unlock the car. I suspect i should replace the batteries soon in both of them.

and i often carry it in the same pocket as my cell phone - so perhaps only the one i actually USE needs a new battery