Hi guys I have a big battery drain , I had a completely dead car one morning. Swapped batteries and immediately 12.8v went to 9v and lower so somethings down to earth . The trouble Is where do you start , I know how to test read across fuses etc to trace current but this must be a failed alternator or something I’m thinking .
Would a mobile auto electrician be worth looking into ?. 2011 tdv8 4.4 vogue Santorini black

Unless the mobile electrician "knows" these cars then probably not.

L322's are well know for battery drain issues. 3 common suspects are ;
Final Stage Resistor
HVAC Control Panel
Headlamp Wiper Motors not parking correctly

There are others. Bear in mind that these cars can take up to 20 minute to "go to sleep" as the ECU's shut down in turn - it only takes 1 to "stay awake" to keep others from shuting down.

A good start would be to get the codes read.

These cars need a battery to be 100% to function correctly.

A good forum search will find shedloads of information.

My 2012 WM drained its battery completely on two occasions, once it was a locking software fault, the other time I think a fuel burning heater software fault. In each case sorted under warranty. The dealer ran a diagnostic check to locate the fault and then sorted the software. The battery needed to be fully charged to be tested as to whether it would still work properly after full discharge. The first time it would not and had to be replaced (under warranty), the second time it was OK. The battery apparently needs to be fully charged before it can be checked.

So unless you find something else obvious get it checked for software faults, and also check whether the battery can still be used. Only Range Rovers since 1988

So yesterday i pulled all the fuses , reconnected a fully charged battery and it went straight to 7v . The original AGM battery is toast at 2.9v and it refuses to charge .
It's obviously got a short to earth , it looks like an alternator failure to me .
I can't get any codes with only 7v in the system , i can't even lock the car so it's going to need recovery for repair .
When i parked it up it was fine no lights on or issues  2011 tdv8 4.4 vogue Santorini black