Let’s assume for sake of discussion that a car’s charging system and alternator are good and there are no drains and that the only reason the 12V battery goes bad is the battery itself.
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Can a good battery tester show signs of a weakening battery ahead of its imminent death? (I don’t want a false sense of security that some of these battery testers can give). I go to some remote places and can’t afford to have a dead battery there, and am thinking about testing my battery before heading out on those trips especially as the battery life exceeds 3 years.
I don't think it happens often that a battery goes from good health to unusable overnight. But near the end of their life, I think they can degrade quickly. Inside, there are delicate lead plates. When batteries charge and discharge, lead crystals are dissolved, and reformed over and over. Over time, the integrity can suffer and they fall apart. The lead can deposit at the bottom of the battery and sometimes even short out. They are especially susceptible if you drive on rough roads a lot.
batteryuniversity.com has some great articles on the subject.
I’m not sure about the battery tester, maybe with the CCA rating?
When I had a failing battery, I tested it with a volt meter. When I got home at night, it was above 12.5 volts. When the car is on, it’s 13+ volts. When I tested it the next morning, it was reading at 11.9 / 12 volts. It shouldn’t drop that much overnight from what I understand. I tried to trickle charge the battery hoping to restore it, but of course it needed to be replaced.
Maybe a battery reader can do this better than just a regular volt meter?
Just a bit of useless information, but my JDM Celsior came with a battery from Showa Denko Materials in Japan. It's a serviceable battery you can top off that was made about 10-15 years ago and that particular model is discontinued now. And it's still in perfect condition. The car is 26 years old, 35,000 miles and hardly ever driven and was transported from Japan > China > America > UK over 5 months in the winter and then sat at the docks for 2 weeks in the UK and the guy told me the car started right up at the docks without charging/jumping. I'm sure they charged it to get it off the ship.
But still, I really can't see the modern batteries lasting like this. Unfortunately the Japanese company doesn't export and I can't find these serviceable batteries anywhere.
