Ford focus had flat battery - charged via another car ignition now turns on but wont start ... its a start stop engine and just says key not detected have tried placing key in central console where the back up key slot is located still nothing have also tried spare key in case its the fob battery .

if putting it in the centre console dont work try 

 

On a point of safety the guy in the video seems to indicate you disconnect the Positive battery cable first. This is wrong and should not be done. In actual fact there is no need to disconnect the positive battery lead.

Simply disconnect the Negative lead and wait 5 to 10 minutes before reconnecting. This will cause all modules in the car to go through there wake-up sequence and in most cases will solve the key not detected problem after a flat car battery.

1 hour ago, unofix said:

On a point of safety the guy in the video seems to indicate you disconnect the Positive battery cable first. This is wrong and should not be done. In actual fact there is no need to disconnect the positive battery lead.

Simply disconnect the Negative lead and wait 5 to 10 minutes before reconnecting. This will cause all modules in the car to go through there wake-up sequence and in most cases will solve the key not detected problem after a flat car battery.

Yes I have always done the negative which is usually the most awkward one to do under the scuttle panel.

Agreed, sorry guys it didnt register, I usually do the neg, but i've also to do the + at some point when i get a few dry days to install a sub.