High FearinLothian
Real sorry to hear about your loss, I have a Phantom 2, and I think I responded to another guy who had a similar problem.
Did your P2 have DJI's ISOD mini fitted, if not, I would say that it an absolute must.
Here's my experience, RC batteries OK, flying in cold blustery weather (say 5° Deg C 8 to 10 Knots wind), bird fly's great hovers, turns, climbs, yaw's the whole works.
Brings her back to land (12 satellites visible on ISOD mini display), coming back in with around 20% battery charge remaining, coming down from 20 Meters, (slow decent)
Yaws about to get nose facing away (I prefer to land that way), drops from 15 meters like a stone.
Fortunately for me, season is late Autumn, really thick heather on the moor so no real damage, gimbal knocked off though.
This type of event happened to me 3 - 4 times, could not understand it, always did compass calibration, did IMU calibration, reset flight control parameters to DJI default, threw away Carbon Fibre props and cheap Ebay props, fitted balanced DJI props, still no joy, every so often the bird would drop, especially during yaw manoeuvres,
Eventually found the problem, the batteries were oldish, 30-35 charges each, but all cells showed good in the DJI assistant,(always stored them at the recommend charge level) but I eventually realised, ( having done everything I could think of ) that the instantaneous drain on the batteries doing complicated manoeuvres, (simultaneous decent, yaw and Forward/reverse stick inputs) when the charge level was around 20% was to much for the batteries.
I still fly the P2 but always bring her home with 25% charge remaining, and limit the number of simultaneous stick inputs.
I also learnt that quickly switching out of GPS mode into Atti mode when the problem occurred, saved it on several occasions, I believe (but more technical Op's may know) that there is more power and thus control available in Atti mode, so pushing the left stick hard forward would allow the Phantom to climb out of a rapid decent even when battery power was low.
I know my story does not help you, sorry for that mate, but it might help others who read this.
Regards Waylander