I looked at all the posts and also the UK Governement Websites, plus the Turkey drone Registration site and finally I went to the airline desk at the airport - here are my conclusions.
1. You are all incorrect and giving poor advice.
2. The battery restrictions ONLY apply to "laptops, tablets and phones over the specified size, and also to devices or battery packs to be used with those items"
3. Drones are allowed in hand luggage, are allowed on Turkish Airlines and ARE allowed in to Turkey.
4. The battery for the Mavic is classed as a camera battery and not subject to the new restrictions.
5. The batteries, being approx 43wh capacity, MUST be carried in hand luggage and NOT in the hold.
6. The new Turkish drone registration system and legality is ONLY applicable to devices with a take off weight of 5kg or over, making the Mavic exempt.
How do I know all this to be 100% accurate? Because I've just returned from Turkey flying from Manchester in the UK, with the Mavic and 3 batteries and had absolutely no issues through any of the security checks. Yes they did request to look at the device and checked the power output of the batteries and said they were all OK.
I'm glad I did my research instead of relying on speculation and now have some great footage from around Antalya to remember my trip with.
Anyone wanting to ask any questions, please feel free. Happy flying and teşekkür ederim!