key not detected message when car doors shut

GET YOUR 12 v BATTERY TESTED.
If it is the original one, 7 years old, just replace it.

 

I have had same issue intermitten and I have a 2010. I just did DX from the screen fir 12v batt and it was giving me 11.1 from sitting overnight. I turned on headlights and it went to 10.9. could this be casue of MPG drop as well and is the onboard DX enough to determine bad batt. I have been checking it now since Sept and same issues but car starts ok and when driving getting 13.6 v not 14 or over like others have stated

 

Yes, not only could be but it's likely. Those numbers are way too low.

Except for the number when running.....but that is the charging voltage and really has nothing to do with the battery itself.

 

ok I will re-schedule with toyota. I just do not want the run around. do you think the 12v is also responsible for mileage drop

 

An "independent" battery shop might be a better place to get it tested.......but maybe not to get a replacement that will fit properly.

I think it is highly unlikely that a weak 12 V will cause a significant drop in mileage because as you saw, the voltage is UP while it is running.
Other factors might be causing the mileage drop. Winter coming on.....low tire pressure......and if you have high mileage on the car, maybe even the HV battery getting a bit weak.