All AGM batteries will hold their charge for very long periods of time. unlike a typical flooded battery which looses charge when stored over time, the AGM's do not loose their charge (negligable charge loss) when not being drawn on. You don't really need to keep an AGM on a battery tender over the winter the way you do traditional flooded batteries. They can also be stored on their side, are spill proof and don't offgas and don't need to be topped off. They recharge faster, the charge can be drawn down very low and fully recharged and this can be done several times. This would kill a typical flooded battery.
In my opinion, Deep Cycle batteries can be easily used for both house and starting. However, I would not really say the same for starting batteries which are really only good for starting. I'm providing links to the Lifeline site only because they're site has a good breakdown in the spreadsheets
http://www.lifelinebatteries.com/marinedeepcycle.php
http://www.lifelinebatteries.com/mar...gbatteries.php
Notice how the Starting batteries only give specs on 'Cold Cranking Amps' which are short periods of high surges of amperage and ideal for turning a starter.
The Deep Cycle includes 'cold cranking' as well as "Minutes of Discharge by amperage". Notice on a deep cycle the amperage draw is typically significantly lower, however it occurs over hours rather than seconds.
Starting Batteries: If you're looking for a starting battery, I base it on the overall size of the motor being turned over by teh starter. The higher the cold cranking the better, theoretically.
House Batteries: This is really dictated by what you run on battery, for how long and how often. I'd add up the total amount of amps for devices that are generally run frequently and for long periods. Consider how long you'll need to draw that amperage, then use this number to dictate the amp hour capacity of the battery/batteries you will need to install.
What I can't answer, and hopefully someone here will chime in, is what the deal is with 6V batteries. I noticed there are some 6V batteries with very high amp hours. You'd need at least two wired in series to make it 12V. I'm not sure how that affects amp hours. It would seem these have very high amp hours, however I suspect the amp hours may get cut in half when wired in series for 12v. I'm just a computer engineer, not an electrical engineer so I defer to any members with more knowledge than me. For that matter, I'll be open to any correction. This is just one guys opinion.
If you do go with AGM batteries, you will need to consider a new battery charger with an AGM option. however, unlike Gel batteries are not as susceptible to voltage fluctuations. GEL's typically require some additional equipment to be able to be charged off of the alternator. AGM is closer to flooded in this respect and can typically handle being charged from an alternator much better than GEL.
Just some thoughts.
OPTIMUM Batteries
Linear Mode
