I will try and amplify one of BFL13'w comments. An extrapolation if I may...
The nearest ATM to where I live is a 320 mile round-trip drive. There simply isn't anything down here. An H-Bomb can detonate in the nearest town and we might see a daytime flash...
So -nothing- I rely on can be expendable. From tires, to battery, to repair parts I cannot afford to gamble. At. All. If I choose wrong I pay dearly.
But some folks live in suburbia where the nearest replacements are perhaps 6 annoying stoplights distant. Shopping? A Saturday project.
For me the choices are set in concrete - None.
But for the suburbanite who plans all year to head to say Yellowstone or Yosemite, then things get a little more delicate. How much is a ruined vacation going to affect the quality of your life? No one else can weigh the pro's and con's for you.
A few years ago I passed through 150-miles of 122F blast furnace and saw zero cars in three hours. A breakdown there could well have cost me my life. The thought did indeed leave an impression. The 122F was in the shade - a broken down car on asphalt would have exceeded 150+F.
As far as my lifestyle is concerned I base everything on - "If it breaks, what's it REALLY going to cost me?" This keeps my decisions sane and based in reality.
When I was working my vacations were precious to me. X-amount of time and even a flat tire was something I did not want to deal with. My bus, Quicksilver has three window type 5,000 BTU air conditioners. Why? The first thought of course was about very limited electrical service. However, the second thought is almost as weighty as the first - If one breaks I have two more. And they can be interchanged.
Batteries decompose in natural fashion in two ways: Electrolytic - where positive plate material is shed during exercising. The second is chemical decomposition. Pure thick lead is very acid resistant but cured plate material isn't. This is why a beautifully floated battery still has a finite lifespan.
The problem is there is no easy way to detect the exact point where a battery goes from "like new" performance onto a decline. The longest lived properly taken care of batteries seem to have the steepest end-of-life declination. From "works good" to "honey where's the flashlight?" in perhaps a week.
The best I have been able to do, is to do a FULL 50% CCA carbon pile load test, followed by a all-cells hydrometer check. I am not merely looking for unequal gravity but looking at the clarity and color of the electrolyte. This is by no means foolproof.
A 90 year old man might be able to walk a mile one day and the next -- well, you know...
I tell myself to "Choose Wisely"