gotcha..One thing about the DD's..they are rated at 12v, which is one of the things to watch for when amp shopping. The reason I buy AGM Deep Cycle batteries is because they are so much more efficient than your regular "Starting Battery" You get the capacity of a much larger battery in a smaller case because the glass mat cells are much more densely packed in the AGM's. This also allows for quicker and deeper discharge and charge rates under heavy load for longer periods of time. The larger wire reduces resistance in the electrical system, allowing the alt and battery to efficiently transfer maximum current flow.
It takes power to make power...you guys just don't know what it was like 25 years ago trying to hustle big boat batteries and finding a truck alt that would fit your car...just to handle 1500 watts of Class A/B power, not to mention the $1 per watt cost for a decent amp.