2018 L405 autobiography just purchase d, how long should a battery charge last if parked up . Mine from full is 65per cent drained after 4 days , dealer says it’s serviceable
But will need jump leads if left at the airport for two weeks on holiday .

Dealer that you bought the car from checked it?
Get it tested by an independent.... then make a decision.
There are gadgets available to do this test.

Main battery type is 019 if you need to buy another. L405 2014 SDV8 4.4 Autobiography
Corris Grey
Previously 2011 D4 SDV6 HSE Santorini

Get yourself one of these.

https://www.amazon.co.uk/dp/B08H8DT2MF

^ that's the gadget..cheap enough.
Have a look at Topdon.
Reasonable prices.

Get the secondary battery tested at the same time.
Type is 096 if you need that. They're circa. £155
019 is about £200.
Brand is personal choice.
I'm Yuasa/ Halfords swayed.
Easy return policy on the 5yr warranty.
Halfords batteries are Yuasa. L405 2014 SDV8 4.4 Autobiography
Corris Grey
Previously 2011 D4 SDV6 HSE Santorini