Battery drained to 4.3 v in 24 hours

What could have drained my battery to 4.4 volts in only 24 hours. The alarm went off but no flashing lights, couldn't unlock with remote. Also can't get in to back yet to check for rain ingress (although ok last time I looked).
...... And what are the chances of both RR's being dead at the same time .. My P38 is poorly as well!!!!

I know I'm going to get 'sarky' answers, and and my friend who worked for Land Rover has also said 'chances of both quite normal

On the L322, FSR failed or, if it has headlamp wipers, the wipers not parking properly.
P38, BECM not going to sleep, early RF receiver responding to spurious signals from WiFi etc.

Update:
Ruled out wet, because it's not been raining for days and all suggested spots dry. In fact no problem - until tonight that is 😁
Not been used again for 24 hours and went out tonight to get in and doors would not unlock - this started the alarm (box drivers side). Battery down to 8.9v - I did go in to boot about 2:00pm and that unlocked - 7 hours later and nothing.
One headlight (offside) pulsing dimly as well
Will now look in to FSR -