Only way to test a transceiver ring is fully working is to see if any fault codes are generated in the relevant module (will be either PCM - Engine, or BCM - Body on a Fiesta I think, or they possibly had a central timer module like a Focus... I just do a full system scan for faults, and that tells me what module it's connected to!).
Provided you get in the transit, and the vehicle gets 12V power, the key will still work to start the vehicle even if the key battery is completely dead. Although the remote and immobiliser use the same chip within the key, the transponder section still works even if the battery is completely dead.
It should take around 5 minutes with the engine running to put enough charge back in the fob battery for the remote to work, so you can't easily put the key in another transit.
If you were really keen, you could split the key and gently put some charge in the battery, but if the key is in good non-damaged condition, you're breaking it's sealing and risking also damaging the key. And at the end of the day, you've still got no back up to get into the van if the remote locking fails again, and to replace the door lock, you're still going to have to drill it out.
Provided you get in the transit, and the vehicle gets 12V power, the key will still work to start the vehicle even if the key battery is completely dead. Although the remote and immobiliser use the same chip within the key, the transponder section still works even if the battery is completely dead.
It should take around 5 minutes with the engine running to put enough charge back in the fob battery for the remote to work, so you can't easily put the key in another transit.
If you were really keen, you could split the key and gently put some charge in the battery, but if the key is in good non-damaged condition, you're breaking it's sealing and risking also damaging the key. And at the end of the day, you've still got no back up to get into the van if the remote locking fails again, and to replace the door lock, you're still going to have to drill it out.