Had the problem twice now but about 3 to 4 months between. Her ladyship copme sin and says cannot start the car.
Turns out the battery voltage is in both cases about 7.8v so rather low.
First time I jump started it and all was well.
Yesterday had same again jump start it and give battery full charge. All okay now except the tailgate will not open except using the key fob. Battery voltage is fine, at the moment.
I am being the pessimist and making the assumption they are connected, though the first time round there was no problem regarding the tailgate.
Read post about adjusting the tailgate switch etc but surely if it opens with the fob the problem lies elsewhere.

Looks like you have a battery drain issue regardless. I had to replace my rear trunk switch which I purchased from my Landy parts guy for a very reasonable price....the 2008 original switch was an aluminum paddle which corrodes overtime, the replacement is plastic so no corrosion issues re the replacement. I had the same problem with the trunk lock, the dedicated fob button would open it but not the double unlock button. I don't think it battery related unless you have a grounding issue. There is a ground on the top right (on mine) of the trunk hinge which does get corroded, easy enough to cleanup and R & R.

Water gets in through the hole in tge glass where the rear wiper blade fits. I replaced mine a few years ago and loaded the gaps with heavy grease... 2002 Honda VFR800
2002 Toyota Celica 140 Silver (mid life crisis - again!)
2007 FL2 GS Manual Army Reconnaissance Green + freel2.com sticker
2004 Toyota Celica 140 Black - Gone
2000 Toyota Celica 140 Silver - Gone
1998 Toyota Celica ST Pearl Green - Gone
1996 Nissan Primera 1.6 - Gone
1994 Rover Montego 1.6 Auto - Gone