Van wont start after fob battery replacement

[CornerwaysUK]

Welcome everyone, I am a new member but i have had a transit van for over 10 years with very few problems until today!
The van is a 2013 Mk 7 transit RWD with Luton Box. It has the blue key fob. In recent past the central locking was working intermittently, a quick look on the internet and I assumed the key fob battery needs replacing which i have done. It is the recharge battery.
Since replacing the battery yesterday the central locking doesn't work from the fob and worse still the van will not turn over (all lights come on but just wont turn over). I assume that the key fob and the van have become disconnected.
My questions are.... 1. Is there anything i can do to confirm that the key and van have disconnected?
2. Is there a way to check that the key fob is actually working or active with the new battery fitted?
3. If the van and key are disconnected how can i get them reconnected?
4. If its likely that i cant do this myself does anyone know who could sort this out for me? The van cant move and i am in Ashton-Under-Lyne
north east Manchester.

Any help would be greatly appreciated Regards Eric

[Altransit]

My best guess is that one, or both, of the van batteries under the drivers seat are in need of replacement, especially if they are the originals

[fortyeight]

you said it was a recharged battery,I'm assuming you used a rechargeable battery,if so no good,a rechargeable battery cause many problems

[Altransit]

you said it was a recharged battery, I'm assuming you used a rechargeable battery, if so no good, a rechargeable battery cause many problems

The key fob battery in a Mk7 is a rechargeable battery, it charges when the key is in the ignition and the engine is running.
Either way, a dead key fob battery won't stop the van starting, as it only powers the fob buttons.