well i got my truck 2 months ago and by looking at the age markings on the batteries they look to be 7 years old. i did a load test on them and they were fine. BTW i drive the truck every 4 or 3 days and the truck fires up fine
I think batteries are a crap shoot anymore. Sometimes you get a good one and sometimes you don't. My Grandfathers 97' 6.5T has only had one battery replaced since new. The other one is original. It has even been driven with a bad alternator for 40+ miles late one night thru VA pulling a camper. The batteries were so discharged it quit shifting.