My L322 (3.6TDV8) Vogue started fine and was running to defrost the car. I was outside scraping off the ice. Car stopped. I restarted it but it kept cutting out after 10-15 seconds. Charged battery and have since had some problems. Car sometimes turns over but won't start, sometimes won't turn over (battery healthy, 12.5V). I cannot get it to run despite connecting an additional charged battery. icar-soft OBD reads a few errors which I have cleared but reads battery voltage as 11.48v.
Parking brake light comes on with ignition but no other lights and when it did start the rev counter did not move before car cut out.

It may be the key transponder. Tried re-synching the key ( car turns over but will not start)
My thoughts are fuel (3/4 of tank)
Key transponder
New battery (18 months old)
Any thoughts or pointers very welcome.

Unlikely to be the key transponder if you can turn the key, that also wouldn't explain why it cut out as security had already been passed to allow a start.
11.48 is very low, try disconnecting the battery and while it's disconnected, give it a charge for a few hours. I'm entirely guessing here but the fact it cut out whilst on defrost could indicate a defective alternator.

Start with a battery disconnect and recharge, then once/if started, do a DTC read again.