Car has been working fine and was in for a complete service & inspection less than a month ago with NO problems.

Now: I was out Thursday night. Car was fine. Went back to the car to drive home and nothing. A few lights on the dash but it didn't even try to start. Tried jumping the car and everything roared to life. Only error was the dynamic headlights showing an error. I used the IID and checked for faults. There weren't any of interest and the headlights reset. The drive home was just fine, everything worked, and the IID said I was gettting 14.0-14.1 V at idle. Parked it for the night. Next morning - everything dead again, including the key fob. (Alternate key fob did work to unlock.)

So, any thoughts as to cause? Battery is a little over two years old. There were no symptoms before the problem started. Mechanic thinks some module isn't shutting down and draining the battery. It seems to be draining very quickly.

BTW About two weeks ago, I started the car after it has sat for 2.5 weeks. There was no power loss then and car started just like I'd only been gone 5 minutes.

Advice much appreciated. I have not noticed anything obvious not shutting down - the cabin lights, headlights and info screen all still shut down as normal (or APPEAR TO shut down).

Doesn't take too much drain to take it past the point where it won't start, what battery have you fitted?

Can you disconnect the battery overnight (don't shut the bonnet as you won't get back in or put a spare battery on it) that way you can see if the battery is losing charge on its own, and rule out a current drain. There is nothing that can't be fixed with a hammer😜😜
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Thanks, NMJ. GOOD ADVICE.

In the end, the car was fine. The battery had given out at only a little over two years with no warning.