Transponder Issues (?)

Hello everyone,

Few months back I started getting a dashboard alert icon w/message "KEY NOT DETECTED" followed by message to place in park, touch start button w/transponder. When this interruption happens, it can take several minutes and tries to get the car started. Last night car started but displayed key not detected message the entire trip.

First response was to presume this was battery related. Replaced the battery, and while issue may have appeared less, it is still appearing. Same started happening for my wife, replaced her transponder battery and message still appears.

Thinking now this either has to be something related to the transponder system on the Prius, or possibly a batch of bad batteries (not sure how to test those little button batteries.)

Anyone come across this persistent issue?

 

I actually have a multi tester .. what settings then for the button battery?
These are new batteries so would be surprised if they are low...BUT..would rather battery than other things.

And if it is NOT battery related, what next?

 

https://www.techwalla.com/articles/how-to-test-a-button-battery


It is odd because there are times, like this morning where the responder doesn't work at all... had to manually pull out key from transponder to lock... and then two hours later transponder working like new....from the same battery. Will test soon.