2005 Prius 12V Battery Questions

I just had a huge epiphany!!

At work earlier, I noticed the battery was at 12.3v so I had nothing better to do, I hooked it up to 2am slow charge on the AGM setting on my battery charger.... after the charge, it was up at 13.4v and stayed there
At this point, my SKS key FOB was hundreds of feet away. So the car was asleep. It had been sitting for hours without my going near it or driving it... .

HOWEVER, at home, I keep my spare SKS key fob in my bedroom (in case I forget to lock the doors, I can just press the Lock button) which is like 20' from my Prius - right at the wall next to the car.

Could the key fob being in such proximity to the Prius be keeping it from going to SLEEP and running down my battery a little over night?? I would feel like such a toolbox if that was the case....

 

"Could the key fob being in such proximity to the Prius be keeping it from going to SLEEP and running down my battery a little over night??"
Yes, you might put the fob into a metal container or wrap it in aluminum foil, if it is necessary to keep it in the bedroom.

 

Seriously? Sonofa$*!@# lol. Maybe this is the reason Im always banging my head against the wall because my 12v batteries dip under 12.2v over night! Ive had the key in the same spot since I bought the car, and I even replaced the battery in the FOB, which probably made it work at its peak range.

I will try wrapping it in foil tonight. Too funny (and just my luck). Glad I thought of it though - I was just sitting here marveling over my Prius and how "smart" it is when I had that AH HA moment.

 

Test your foil wrap process by taking the wrapped fob out to the Prius to make sure that you cannot lock/unlock the doors, with the fob nearby. You need sufficient overlap on the foil so that no RF energy can penetrate the foil wrap.

 

Gotta love these epiphany moments, hehe
I know the solution sounds a bit "tin foil hat"-ish, but I think it will work.

I don't have the sks option on my Prius so I have no personal experience with this, so can someone tell me what is the approximate range of the smart key? I would have thought a lot of people could potentially be in the same situation.

 

The Smart fob will attempt to maintain communications with the Prius at around a distance of 15 feet or so.

The Smart fob needs to be within a few feet of a Smart receiver for the car to allow the door/hatch near that receiver to unlock or lock.

 

Interesting. I wonder if being just on the edge of its comms range could be even worse then being in constant communication? I mean if connection frequently dropped out and reconnected throughout the day, possibly it could keep waking it and make it more power hungry.

 

Yes, a reasonable possibility.

 

You didn't watch the battery voltage long enough.
A 13.4 reading is from "surface charge" and will bleed off fairly quickly.....like within an hour.....down to
the real resting voltage that will be something between 12.4 and 12.8.

My manual says the FOB has to be within 2.x feet to be activated and recognized.
20' should be plenty to NOT be recognized.
My FOB has a tiny red light that flashes when you are close enough.

Note that pushing the buttons of the FOB will work a LOT farther away than 3 feet......but that is a different function.

 

There is a difference between the fob distance required for the car to unlock a door; vs. the difference required for the fob to establish communications with the car. The latter results in increased current drain by the Prius ECUs although there is no apparent change in behavior when viewed by the casual observer.