battery life

When you get 8 full years out of a battery with it failing in the 9th year, why switch to anything else. I might get another year or two if I didn't forget to hook up a battery charger/maintainer the odd time. After the factory fitted Mareg battery failed (after 9 years), I replaced it with...

I know there is no real answer to my question but I am hoping for "an order of magnitude" result. I have operated with many "rules of thumb" such as change your oil every 3000 miles. Now my Toyota needs changed at 10,000 miles. As such I realize many of my old rules are outdated. So, here...