Parasitic drain advice wanted.

[jepotherepo]

Hi - for some reason the search function isnt working so I’d appreciate some advice regarding my battery on my t5 beach.
Main battery (3yrs old) fails to hold charge when vehicle not driven for a few days. Drops to 12.2v ish. Does this despite being previously charged on my optimate or after 3hr drive.
Could be battery failure but am considering parasitic drain. Anyone got advice on likely culprits to check?
Alternator appears to be working fine - creates up to 14.8v when driving And blue motion active.
thanks