I am puzzled by what you say about "off the shelf" deep cycle batteries are glorified car batteries. If so, there is allot of fraud going on out there. I can't believe that. I can believe that there are different levels of quality in batteries. If I am shopping for a deep cycle battery I would buy one that is well known and sold everywhere because of warranty issues. If I buy an Interstate battery in PA and have a problem in FL I can find a dealer quite easily for a replacement. I have had Interstate deep cycle batteries for many years and have never had a problem with them. IMO
The 2 articles you provide links to both say that "Deep Cycle Marine" are most likely just a Hybrid battery;
Quoted from the first link -"Marine batteries are usually a "hybrid", and fall between the starting and deep-cycle batteries" = "Glorified Car Battery".
So when you go and buy a "Deep Cycle/Marine" battery off the shelf, you are for lack of better terms and without cutting the thing apart, buying a "Glorified" car battery...
You either want a "Deep Cycle" or a "Starting" battery, but you really are NOT looking for one that does both...
The Devil is in the terminology; (Quotes from the first article)
Starting - (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines.
Deep Cycle - batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates.
Marine - batteries are usually a "hybrid", and fall between the starting and deep-cycle batteries, though a few (Rolls-Surrette($1,190.29 AND WEIGHS IN AT 272LBS and won't fit in the battery box) and Concorde ($253 for their "group 24"), for example) are true deep cycle.
So when you Combine "Deep Cycle" and "Marine", like is the case with a lot of "off-the-shelf" batteries I have seen in stores, you are most likely just getting some kind of Hybrid.
This also goes to "you get what you pay for" - I can buy a "off-the-shelf" deep cycle/marine battery for about $100, a true deep cycle (Deka for example) is going to cost me a little over $200... but the Deka is a "true" deep cycle battery... When they combined the words "Deep Cycle" and "Marine" what they should have done was slap a label on it that said "Glorified Car Battery" and it would havve been a lot closer to the truth.
I have been looking into solar panels for some time, I was planning on building a "off-grid" house for about 5 years now and have read many articles on panels, batteries and controllers. One thing pretty much rings true from what I have seen; If a battery has a CCA = (Cold Cranking Amps) rating on the label, it's some kind of car battery... The term "CCA" is not used in a solar apllication...
And RichR I am not trying to beat up on Interstate batteries, both my vehicles have them in it and the last 2 that I have sold had Interstate batteries in them, the last truck I owned had a 6 year old Interstate battery when I bought it and I owned it for 5 more years... Yup 11 years on a 72 month battery... just beware of the terminology.
A Deep Cycle/Marine battery is a "Marine" battery designed to be "Deep Cycled" just not to the extent of a true Deep Cycle battery.