Pre-emptive replacement of batteries isn't crazy talk. You can actually end up killing your alternator if you don't catch a dying battery. I made it 6 years on my trucks batteries that it came with from the factory. I didn't have any issues with starting or charging, but once you get to 6 years on a battery, you're living on borrowed time.. My truck is diesel and has 2 batteries. Sure enough one of them was leaking when I pulled them.
Had the 8 year old F350 diesel in at COSTCO getting the tires rotated a couple months back, hot summer weather. The tire shop manager told me it was done and to get the truck outside the shop. The tech walked out to me and says do you have starting problems with it, because it won't turn over? We put it on charger for a bit and it was obvious the batteries were done....originals that had done well for 8 yrs. I went in the store and bought a couple and they loaned me the tools to install them, (no tool kit, nor the jump pack as I was just going to COSTCO for an hour both were in the other truck). What a convenient place to have the batteries quit compared to where I was bear hunting with it a month earlier...5 hours from a replacement option and 15 hrs from home.
Just changed mine last weekend for my trip out west. $200 is a small price to pay to ensure my truck starts in below freezing temps when I need to head home.