I like Fred W. of USB, he is a really bright battery engineer who knows his stuff.. However, the data they claim is not entirely accurate nor is it entirely honest in regards to the 24, 27 or 31..
Think about it, USB is suggesting/claiming/marketing that their G 24, 27 & 31 "deep cycle" battery is TWICE AS GOOD as a Trojan and THREE TIMES AS GOOD as a Deka/ East Penn. This is on par, technology advancement wise, to the Carbon Foam Firefly in terms of performance gains. Independent test data does not back these claims up. I put the USB 24, 27 & 31 right up there with Trojan, which are slightly better than Deka. When you push Fred on this issue he will fully admit it that the data for the automotive sizes is not really what they claim or suggest it is in the "marketing" speak...
The 12V Group 24, 27 & 31 are certainly comparable to the Trojan Group 24 (SCS150), G27 (SCS200) and G31 (SCS225) but Trojan is actually
more honest in their lab data claims. Lab data is actually meaningless in the real world too but can give decent guidance within a brand, for durability and cycle life guidance, if that manufacturer is not BSing..
In my experience Crown, US Battery and Trojan make some of the best 12V
automotive type batteries but they are not going to
cycle comparably to a GC or industrial type battery. FWIW these three are the ONLY automotive style "deep cycle" batteries I have tested that have ever met their Ah ratings and even then it is quite rare.
I have not tested a single flooded Group 24, 27 or 31, from any other manufacturer, that could deliver its rated Ah capacity when new (7-12 cycles), broken-in 15-60 cycles) or slightly used (1 seasons use). I have tested GC2 batteries and GC12 batteries from almost all makers and seen them hit Ah ratings much more reliably.
I was recently talking with the lead engineer for a large US manufacturer who is working on a new battery monitor. His exact words were;
"I've yet to test any 24, 27 or 31 battery that has delivered it's Ah rating. This is a real stumbling block we are trying to over come in the learning algorithm. We are being forced to do this to avoid the inaccuracies of unquantified owner programmed ampere hour data."
If a Group 24, 27 or 31 is all you can fit you really can't go wrong with US Battery Trojan or Crown. If you can fit a taller battery, go with a battery designed from the ground up for cycling purposes. It will cost less over the long haul.
For a good read look up Trojans responses to USB's rather inflated marketing claims...:laugh
Both Trojan and East Penn are quite a bit more honest in their lab cycle claims than USB (USB still builds a good battery). All battery makers are a bit sleazy, as is the BCI, who has whole heatedly resisted any sort of PSOC ratings, fair cycle-life ratings or honest labeling practices in regards to cycling batteries. It's no wonder because the BCI is driven by the battery industry. Sadly the EU has eclipsed the US in more equitable battery testing data. Until the industry becomes honest about their ratings we have to learn to wade through the bovine dung.
The fact that a battery lasted "9 years" is actually rather meaningless unless we know what its Ah capacity was along the way. I can point to many auto type batteries that have lasted 10+ years, if I completely ignore actual end of life Ah capacity. With light loads, shore power most of the time and pretty much constant float life even an automotive type battery can easily last 9 years. By industry standards it has likely been dead for a while but under light loads they can certainly last beyond the 80% end of life industry recommendation. Problem is that once below about 80% of "Ah rating" I start to get more messages and texts like this one I got a few weeks ago..
Everything is a compromise and fitment is one of those compromises because builders have forced us, through molded trays etc., to use batteries that are not well suited for the usage we are often doing. Tied dockside most of the time, these batteries do okay. Put your boat on a mooring, like most of the North East and the Maritimes, and these batteries simply don't match the performance a GC 6V or 12V or industrial type battery in terms of longevity.