not anything other than my experience but i have found that allowing the deep cycle marine battery to stand up longer by allowing it to totally discharge and then slowly recharge (I use my 6 amp charger) for 24 hours. I have usually gotten 5 years out of my batteries.
Hate to disagree, but I skimmed through to see if someone had already offered the opposite advice, which I believe is appropriate. Even Deep Cycle batteries will perform better, the less often they are completely discharged. Something about the build-up of crap on the plates. Using only 20 to 50% capacity is ideal, but at most you might expect to double the life of the battery anyway. As a rule of thumb; I'd simply charge it each day when you're done using it.
AH is simply Amp Hours, and you'll find BIGGER batteries will offer higher AH numbers. 12 VOLTS is what the machine runs off of, and it will not know the difference... except for BIGGER is HEAVIER, obviously... and it will last longer in roughly the same ratio as the AH is greater, minus a little for the added weight you'll be hauling around for it. Do note that any deviation from the manufacturers battery spec may require a change in battery connection (which any handy person could do in minutes.) Also note that any size/power upgrade will probably not fit in the little compartment, so you'd have to sacrifice the sleek looks for better function.
If the machine doesn't seem to be struggling with the load now, I would be tempted to change out the connections, if necessary, and replace that little specialty battery with a more standard Marine Deep Cycle Battery, as they are considerably cheaper and should last A LOT longer. Something like THIS
. That one's available at Sears for $70 (with trade in), but you can find a similar battery just about anywhere car batteries are sold. I would expect much better performance with such a battery, for a lot less money, because it is so much more widely used and competition mandates the quality/cost ratio be a good one. The example I linked comes with a 1 year full replacement guarantee, 2.5 years pro-rated replacement if (when) it eventually weakens.
Finally, if you do move to a standard battery, you'll probably want to invest in a "smart charger" as well. A smart charger begins by rapidly charging the battery at the beginning of the charge cycle (which is good for keeping the plates clean), and then slowly eases back to a trickle charger as it gets closer to fully charged. This offers the speed of a quick charge, with the quality of a slow charge, and will actually extend the life of your battery. These machines can also be used to "recondition" a battery when its performance begins to slip.