my son has a new shape fiesta and today he could not enter the car either with fob or the mechanical key. a mechanic suggested getting power to the car from underneath. is there any way to get power into the car so that we can release the doors. as my son is willing to smash the window so we can open the  bonnet to charge the battery.

Why would the key blade not work? It's a mechanical lock so should work if there's power or not.

we tried turning the lock you could fell the mechanism moving but it would not open, if we turned it any harder his key would have broken

That does not sound right. Check online for the instructions first. The lock should move and the latch free. It might be cheaper and more convenient to damage the grille instead if you need to open the bonnet. A locksmith would be a better solution.

This may be nothing but from a US poster:

I'm pretty darn sure that if your turn the key and pull the door handle, the door will open. I think you were waiting to hear the solenoid click, but you won't hear that because your battery was dead. Turning the key overrides the solenoid.

went out this morning and turned the key anticlockwise with a firmer pressure and the lock released. he has a flip out key and it feels like it is going to break the key it was that stiff last night. i did put wd40 in lock last night . so big sigh just need to get a charger now. thanks for the help.

 

Definitely locksmith a better and cheaper option but hire those lock experts who deals in auto locks and keys.