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never looked into it much but story I was told is that regular batterys do not liked to be sucked completely dry and that a deep cycle will survive that treatment a bit better
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Correct, it causes plate erosion and kills the acid in the battery.
A battery will usually come back if:
You didn't wear out a plate and/or cause a plate to oxidize and the plate fall off and short out a cell
You didn't overheat it and ruin the chemical energy storing component of the battery (whether it be conventional acid or not). If it vents a lot of fumes you overheated it.
These days, it's usually plate failures that kill a battery in an offroad rig. The rest of the time it's sulfation. Sulfation happens when the sulfuric acid (chemical energy) converts to electrical energy on the plates. Sulfation, if not converted back to regular lead, can sometimes become a crystal on the surface of the lead plate in which it's difficult to get a battery to take a charge. This process of sulfation can cause plate failure. Basically, the sulfate on the plates isn't uniform and you'll only use part of the plate. This "wears" the plate thin. If you slowly charge a battery, no matter what kind, it causes the "sulfating" to be more uniform. This is why deep cycle batteries require slow charging.
Anyway, I'm tired, and I have an emag exam to study for.