2013 sd4 xs, flat battery, tail lights stuck on . Opened door with key , jump start OK. Radio, nav, blue tooth ,rev sensors and camera all inop .checked numerous fuses. Disconnect battery earth , refit and everything works for 1/2 hour then it all stops working again. Any ideas?

Fully charge the battery with it disconnected. Then see if it all works after reconnecting the battery. 2009 Rimini Red SE TD4. Soon to be sold.
Hyundai Ioniq 5 Ultimate on order.
Gone. 2006 Tonga Green i6 HSE.

Drove for 3 hours, battery halfords tested en740 at 738amp , so I would presume battery is ok

Driving for 3 hours does not necessarily fully charge a car battery and Halfords testing isn’t regarded as the best. Try following the previous suggestion. Disconnect the battery and put it on charge overnight. Reconnect and try again.

Removed earth lead charged battery all night, reconnect earth drove for 1 hour everything fine, parked for 1 hour and now not working

How old is the battery? Over 3 to 4 years?
It may not have all cells working correctly.

You may need to do some voltage checks after it, been charged, has stood for 24hrs, before - after and (if possible) during start up.
If not charging at about 15v, then check blue wire for damage (monitors alternator).

Random faults will occur if enough power is available during start-up initialisation. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)