Well if research is done it would be known that starting batteries need to be maintaind at around 12.6 volts.Otherwise the cells inside will die, so if there is anything preventing that count on having a dead battery.
A alternator is no meant to charge a battery from a drained status, it is meant to maintain the battery at the proper voltage. A deep cycle battery is more forgiving because it is designed to be drains and charged for many cycles over and over again but in time it to will fail. Sometimes there is batches of bad batteries where the mixture of chemicals was wrong from the manufacturer and there was a flaw in the design. Even if a battery gets dropped or is not held down may cause it to fail.
Batteries are sensitive to vibration unless you want a optima for 200 dollars.
Many things can cause a battery to fail.Do your research and then purchase the right choice don't let sensitive people make it for you.
Reason of review: Good customer service.