Originally Posted by Donald
Originally Posted by CT8
It depends .
+1 it depends.
Now if you used a carbon pile load tester every October you would probably never be surprised with an unexpected battery failure. (October was picked due to winter. Florida may be different).
Another +1.
I've had one unusual experience not listed above. My previous '97 Legacy used to kill its Yellow-top (deep-cycle) battery relatively frequently, but it would always recharge and last for months before having it go dead again. It would literally crank fine one time, then, during the next crank, it would have just enough to slowly crank over, but not enough to start the engine. The previous owner had installed the yellow-top before I took ownership. I'd only ever used deep-cycle batteries for boating (e.g., trolling motors, back-up/starter batteries, etc.), so maybe that's why it was so unusual for me to live so long after so many drains...
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Outside of that one instance, I've experienced batteries that would die after too many jumps (before I knew better than to simply jump and drive...); I've experienced a battery that simply died after previously operating normally (Honda OEM); I've also experienced batteries that slowly degraded (past couple of Subaru OEM) --> they would test fine, but would crank noticeably weaker from winter to winter.
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Since then, I've made it a habit of charging our batteries to full at least a couple of times per month, weekly if I can help it. I use a DC power supply to ensure an actual full charge. It's amazing how low of a charge these batteries get to. Our Legacy had to be re-flashed due to a TSB for too little charging from the alternator, resulting in too many dead batteries. Even after this reflash, it's still not perfect; better than it was, but not perfect. The Forester will have a battery at ~12.35VDC after a couple of weeks, and take 1A of charge for hours before reaching 14.4VDC, then take 14.4VDC for more than a day before showing a completely full charge!
I don't use really any gizmos or heated seats or the like, unless my family is in the car with me. I simply don't need them. My wife's Foz, however, has a lot of heated things and probably draws a ton more power during her driving, which is likely the cause of the lower battery levels. That....combined with a likely poor charging logic from Subaru to save 0.1 MPG...
I my practice of fully charging the batteries every so often helps them live a long live; however, it won't matter if a cell shorts! I could charge them every single night and it would all be for naught, if a cell shorts tomorrow...