Odyssey batteries do currently have a great reputation.
Sears Die hard PLATINUM is a rebadged Odyssey and about 25% less $$$.
I am not sure the internals are 100% the same though.
In an ideal world, all batteries that connect, charge and discharge in parallel would be the same brand,design, and age. But it is not an ideal world.
Hooking batteries of different ages and make in parallel works, but one battery usually takes on more of the load and charging source than the others, and when one goes nearly dead, it drags the other down fast, then you need to buy 2 new batteries anyway.
The most important thing to battery longevity is to promptly and fully recharge them after discharge. The alternator does an OK job at bringing them to ~80% but it would take many many hours of driving to top them off to a true 100%.
Recharging to only 85% time after time will cause progressive sulfation and capacity loss. Any time a battery is sitting below 80% it is sulfating, and the lower it sits below 80% and the longer it sits there, the harder the sulfates become and the more capacity is lost.
The Batteries best friend is an automatic plug in charger that will bring the voltage up to the high 14's for an hour or 2 or more to squeeze in every last amp and dissolve the sulfates back into the electrolyte, as much as possible.
Flooded Batteries self discharge 15% a Month at 75 degrees, more at higher temps and more with age. AGM batteries like optima and odyssey are about 3 to 5%.
A Float charger is good just to keep a fully charged battery topped off. A float charger is not good at topping off a battery as they usually cannot bring the battery into the high 14's.
Keep in mind that a healthy battery that is only 30% charged will still start the engine, so thinking that the battery is fully charged cause it started the engine is folly.
Another thing to be aware of is the Marine Battery. These will also say Deep cycle on them, but the difference between a true deep cycle battery and a marine battery is significant. A marine battery is sort of like a starting battery which is slightly more tolerant of deeper discharges than a starting battery. It is not easy to find and purchase a true 12 volt deep cycle battery, and they are about 30% more $$$ and about 20% heavier.
Crown, Trojan, and Deka among others make true deep cycle 12 volt batteries, the hard part is finding them. Whether a true deep cycle battery is worth the extra 30% premium depends on how well you intend on taking care of the batteries. If you are not going to make sure to fully recharge them promptly after use, then the marine batteries might be cheaper in the long run, but if you do take care of them, true deep cycles will perform better for significantly longer.
Generally, 6 volt flooded golf cart batteries wired in series are the best bang for the buck. They have the the thickest plates, and enough room under the plates so that when they start shedding material, they take a lot longer to short out a cell.
But they are taller, and must be vented and are not good for the inside of the Van unless properly vented.
AGM batteries only offgass if extremely overcharged, but still, technically, should be vented to the exterior.
Increasing the thickness of the alternator charging circuit is vital when extra batteries are added. The stock wiring is adequate only to top up a slightly depleted starting battery. Add a deep cycle battery over another 20 feet of undersized cabling pretty much insures chronic undercharging, early sulfation and a premature death.
Also, it is good to have a plug in charger capable of at least 25 amps. The battery can accept this much and more when depleted and when it nears the 80% mark will accept only what it can take.
In my Experience, the batteries like heavy current initially when discharged under 60%, and perform better the next night when they themselves dictated how much amps they wanted, rather than an undersized charger taking longer to bring the specific gravity up above 1.275.
My 200 watts of solar (~ 12 amps) is great at negating discharge and still fully charging them during a sunny day, but if I were to hit the batteries with 25 amps for 2 hours in the morning, then let the solar take over, the batteries will hold a higher voltage the next discharge cycle.
Idling a Dodge to recharge the batteries is an extreme waste of gas. Do not bother, as little as 5 amps are making it into the batteries with a hot alternator at idle speeds.
The following charger is spoken well of over on RV.net:http://www.amazon.com/Black-Decker-VEC1093DBD-Battery-Charger/dp/B000EJQJ1G.
If you use the batteries a lot, then the above charger will help you get the most out of them.