Things that will destroy a battery

There are essentially two things that will quickly and easily destroy your battery: 1) undercharging it or 2) overcharging it. The majority of deep cycle and starting batteries are lead-plate batteries filled with sulfuric acid. Undercharging them will ultimately cause lead sulfate to accumulate on the plates – this will eventually destroy the battery because the normal chemical reaction will be unable to continue. Overcharging the battery will accelerate the natural corrosion of the plates due to excess electrons being literally boiled out of the electrolyte. Ultimately, the fluid boils away and the plates are exposed to the air, which ruins them.