range rover battery drain engine immobilized

Hello my dads range rover is starting to take a toll on him.
The alarm keeps going off in the night.looks to me as if there is some sort of battery drain which when it gets low the indicators come on he then tells me the battery is now flat as a pan cake which immobilized the engine.we have called out range rover who get it started for us and tell us there can't find the problem
We have had the door locks changed because they would not unlock the rear doors by range rover who fitted new locks for 600 all in and they still don't work
Is they a small fuse i can change to sort all this out for him lol
help please

RF receiver

use search - will be a lot of info on this!!

(just done mine same fault)

^^^^^^ What He Said....

As above plus dodgy battery/low voltage.