[Excaliber]

Deep Cycle batteries, unlike regular batteries, will force your alternator to put out as many amps as the battery can take. Deep Cycles are amp hungry! In some cases this leads to premature failure of your charging system from meeting that high demand rate for an extended period of time.

Worst case scenario would be, engine doesn't start, so you crank and crank the starter trying to figure it out and run the Deep Cycle battery pretty low. When the engine does start, the alternator will be putting out near max amps for quite awhile bringing that battery back up to speed.