Juicygalaxy

Hi everyone I'm new to the forum and could do with some advise. Problem started last year in the cold the wife calls me to say battery flat on the Galaxy. No problem charged overnight ok for four days then same again. I eventually changed battery which helped a little but then the weather warmed up and was fine. It has now come back to bite me in the bum as last week same phone call blah blah blah. Took it to my mechanic said battery fine alternator fine but a drain on battery turned out to be interior lights and power sockets so removed fuses thought job done for now. How wrong I was as had the dreaded call this morning. So I got home she jump started straight away I let her run for only 5 min turned her off bugger me she started!!! I put battery on charge and charger saying fully charged within an hour!!! Is this right? Had some random know all say it's yer battery mate but I don't want to invest in one if not needed. Starting to drive my dearest up the wall