Steve brings up a good point on the replacement cost of batteries, but one thing that needs to be considered is the rapid advance in battery technology. I am old enough to remember "D" cells with a carbon rod through the middle. Compared to Alkaline cells thirty years later, or NiCads, or Lithium cells, or the LiFePO4 units, the increase in performance is quite impressive. However, as with almost all new technologies, some hazards will always exist. Modern batteries are energy storage devices, and the amount of energy that can be released through misuse or damage can definitely rearrange your priorities. ("Run Away!")

When I was racing cars, a simple aluminum fuel tank was deemed sufficient. And then fuel cells with puncture resistant internal bladders became available. The were mandated (over protest, naturally), but I don't know of any drivers that would prefer to go back to the "BBQ Days."

It is conceivable that, by the time your batteries need replacement a newer, safer and more efficient solution may be available. Personally, I am holding out for the "Mr. Fusion" reactor seen in the "Back to the Future" movie..