Changed 12V Battery - Now Key Fobs Barely Work

There should not be a connection between the 12V battery and the key fobs, assuming the new 12V battery is properly charged. Of all the 12V battery replacements reported on here I have never heard of an issue with the key fobs.

Having said that though, if after replacing key fob batteries you still have issues I would definitely take it to dealer and explain your issue.

 

I also can not easily think of a direct connection to how changing a 12 volt battery and Key Fob failure would manifest.
But I would say this, and I may be wrong, others can chime in and correct me.

But I was told it was "wise" to replace both fob batteries at the same time even if one isn't being used. The presented logic being that the Prius "smart key" system operates by the fobs more or less giving off a constant signal. That's how the vehicle "knows" you have approached even with you not pressing anything.

Battery cost in this case is minimal, so recently I replaced both at the same time.
There are numerous youtube videos that show how to open the fob and replace the battery. Relatively painless procedure.

It certainly is odd that you would manifest this symptom after a 12 volt battery replacement.
Good Luck, and out of curiosity, let us know how this story unfolds.

 

If anything could have gone wrong.....it would be when the car was jump started. There is no relation to changing the 12v and the keyfob not responding

 

I bought a new smartphone recently with a rubber case. I tend to put my keyfob in my pocket along with the new phone.

I started to notice many keyfob not detected errors. Other times, it couldn't sense the keyfob at all. This was caused by my new cellphone. it was covering my keyfob. Removing the cellphone solved everything.

You may want to check if there is anything in between your fob and the sensor (like my cellphone). There is a different sensor inside the car and outside by the door handle. I would examine to see if there is a diffference in sensitivity between the two sensors. There is also the possibility that your fob batteries are getting low.

 

make sure the battery connections are tight and clean at all 3 points. but i would say if you went to the dealer to have the battery replaced, they should look at this problem gratis.

 

Yes. Could be the new battery is a lemon too. Do you have a digital voltmeter, try reading it's at rest voltage?

Not sure of the ramifications for the fob reception, but does seem fishy.

 

New cellphone or radio tower in the area where you park your car?

The 12V battery should have no effect on FOB range.

 

A year ago I had the low key fob alert. Went and had a new one put in and two months later the 12v. died. Had it towed to dealer and a new one installed. 6 months later low fob battery alert, I get a new battery, still alerts, changed fobs with hubby, still alerts, got new battery for that fob, still alerts. Went to dealer for service (tire rotation/oil change) and mentioned the problem. They put my fob on a meter and it read "strong signal". I said I am worried about being stranded again, they said it is not related to the 12v. Now car would not open (had to use key) and had to place fob on button to start. While driving it said "No key detected". What could it be?