Download the"Airmap" app it shows all nfz's, including temporary ones, and also displays notam's. ( Notice to airmen). You can filter it to UK data only.
Flying in fog at 0 Deg temperature almost certainly led to icing on your props. This would cause the motor overload, erratic flying behaviour and eventually the failure of the flight altogether.
Why not pack 3 batteries plus the charger?
Takes up the same space, weighs the same and covers all eventualities.
( Or even just 2 batteries plus the charger).