Mine used to last 2 or 3 days Couldnt find a power drain and the battery tested ok.

Got totally pissed off with it never starting so i fitted the biggest, most powerfullest fook off great battery I could possibly fit in the tray - Job done, havent flattened it since.

(Its an Exide excel battery for a Granada 2.5 diesel)

Lasts anything up to 4 weeks now, still bursts into life!