Remote key is completely dead, I can only use the blade key to manually unlock the driver door. Central locking from the dash is also not working. When I try to start the car i get "smart key not found" message.

No water ingress that I have noticed at least.

I will check fuses, the battery has been disconnected/connected after charge and nothing happened.

I will also have a go at bypassing the battery and connect starters directly to the wires.

Hopefully a mate is coming over this afternoon to check battery with a meter. RR Vogue 4.4 TDV8 - 11
Toyota Land Cruiser Prado - 02

LR Discovery 4 SDV6 -11 - Gone
RR Vogue 3.6 TDV8 - Gone

So, tow truck came this morning to take the car to LR for diagnostics. Reconnected the battery after 8 days and the car started just fine with everything working

Tow truck turned around and went home.

Drove to local garage to check fault codes but nothing serious and they all cleared. Fingers crossed problem wont come back....

Thanks for the help and suggestions everyone, absolutely no clue what worked and not...Guess it´s just one of the features of a Range Rover  RR Vogue 4.4 TDV8 - 11
Toyota Land Cruiser Prado - 02

LR Discovery 4 SDV6 -11 - Gone
RR Vogue 3.6 TDV8 - Gone

Only a couple if things I can think of:

1. Loose battery connection to the poles can leave your car dead, even with a full battery, even when they appear tight.
2. Check there isn't a second battery in the back somewhere which may be draining your front battery or causing a short.