Car Battery Draining?

I have gone through 2 brand new batteries "now on my 3rd" from Advanced Auto. We have a 2000 ford windstar 3.8. I don't know what is going on. The battery we had before this year lasted almost 6 years. It was a autozone battery. Seems like the advanced batteries only last about 3 months and then go dead. We don't do alot of driving. Mainly my wife uses it. Today I took the vehicle up to autozone "one week after owning this new battery" to get it checked out. The guy had hooked a meter to the battery and said it was 12.30v. Last week it was 12.65v. He tested the alternator and starter and said they all work and not showing anything wrong. My neighbor said that the autozone guy should've checked the battery for crank by turning the van on. He didn't do this. He started the vehicle to check alt and starter. Is this correct? I don't have anything installed in the vehicle,and turned off all the inside lighting including the dash lights just incase this was causing the drain. The van hasn't had a problem starting,but after going through 2 already,I am worried about my wife being out and it not starting. One thing we do have and not sure if this would affect anything is our belt squeeks and chirps. The mechanic at a local garage said the tensioner is in need of replacement but its okay to drive on. Just have to deal with the noise. He also put a bar of hand soap on the belt. I haven't done that and don't know why cause the chirp came back. Could this cause battery drain?

Any help would be appreciated. Just wasn't sure if the guy properly checked the battery.