MasterVolt is likely relabeling another maker's, and while a quality brand, is rarely a better value - need to compare price per AH, but reputation is tge most important.
Mastervolt is not relabeling, made in Holland as I understand it. Marine electronics dealer in Seattle told me they are great, unless there is a problem, then it takes forever to resolve or replace. He recommended Lifeline, evn though he is a Mastervolt dealer.
How long did you get? Where you coddling them?
Averaging about three years each on the Odyssey G31s. First one developed a dead cell right at the three year mark. Second one failed to take a charge at about three+ years. Third one is in the truck now, will be three years old next month. Won't take a full charge, won't hold a charge for more than a couple of weeks. No measurable parasitic drain, beyond spec. First Odyssey was not coddled, just plug and play. Second one treated respectfully, run on conditioning cycles periodically with 40amp Odyssey smart charger. Third (current) one has been coddled, started with conditioning charges every month on Odyssey 40amp charger, then progressed to frequent conditioning charges on new Odyssey 20amp smart charger, now gets a full conditioning charge every week or two, will not take a full charge. For the first year or so, I kept a detailed log of SOC, charge cycles, dates and miles driven, etc. After the first couple of months, battery would not get to or hold a full charge at 12.86 resting OCV, all in the log. Decided logging all this data was a waste of time.
AGM just don't last as long as FLA, and their charging requirements are much more demanding, easy to murder them early.
Have had numerous phone calls with Odyssey tech support and I am doing everything by the book. No murdering going on here.
Do you actually **need** sealed?
I actually need high capacity for the starting battery, and need AGM for the house batteries because they are mounted on their sides under the truck. Lithium ion is not an option because this is mostly a desert truck and they don't like the heat.
Where are you located?
I'm in So Cal, not all that far from the Lifeline factory. Lifeline is not answering their phones today. Lifelines appear to be dual purpose AGMs, but with better ah and worse cca than Odyssey or Northstar.