Apologies for the "delusional" remark, my bad. I have heard some pretty tall tales on this Forum over the years and many involve magical batteries that last seemingly forever but then I have read here about brakes lasting 200,000 miles and Mercedes diesels that get 20+ mpg...
The southern California Trojan rep made the 3 year planned obsolescence comment about 20 years ago... I'm sure they are probably better now though not much has changed in battery technology. The Chandlery I worked in was selling dozens of Trojan golf cart batteries every month for use as the "House BanK" on cruising sailboats.
The battery industries business model is based upon people replacing their batteries every 3 - 5 years. The better the care, less abuse and use the longer they will last. Yep deep cycles tend to last longer as most get far less use in the real world.
If you have a high tech multi stage charger, perfectly maintain the electrolyte levels 24/7/365 and use them very little I guess from what I read here just about anything is possible. On boats they are in hard use 24/7/365 as most are driving DC refrigeration systems along with radars, auto pilots windlasses etc..
My point is very few RV'ers are huge consumers of DC power and quality deep cycles, when properly maintained are very reliable. Any deep cycle battery has a finite/fixed number of deep discharge cycles built into it and nothing can change that number. When you have completed the rated number of deep discharge cycles the performance of that battery will begin to deteriorate. If a battery has made it to 10 years it has not had many deep cycle discharges over that period... you cannot change the physics of a wet cell battery.
As always.... opinions and YMMV
:C
