You really need to stop looking at batteries based on physical size
and look at the "intended" use.
The only 4D & 8D batteries I am aware of, marketed in the US, that are actually available in a true "deep cycle", are the following:
4D & 8D
*Dyno 4D & 8D Deep Cycle
*Deka / East Penn Gel 4D & 8D (private labeled to many other brands)
*Trojan 8D GEL
I may have missed one but have not had my coffee yet.. Every other 4D or 8D battery out there is really a dual purpose
truck battery NOT a true deep cycle battery.. 4D & 8D are best optimized for starting large diesels NOT cycling applications. They are also well optimized for keeping your spine surgeon in business.
There are big differences between typical 12V "marine batteries" and 6V deep cycle batteries in terms of cycle life, which is really what you want.
batteries one must consider well beyond just Ah capacity. The most critical aspect to longevity will be the cycle life or how many cycles to 50% DOD you can pull off.
Most all 12V "deep cycle" marine batteries are imposters
including top end brands like the Trojan 12V G-24/SCS-150, G-27/SCS-200 & G-31/SCS-225... They are not a true deep cycle battery and will yield far less cycles than a 6V GC2 battery. Trojan rates the SCS "deep cycle 12V line at about half
the rated cycles as their own 6V T105 golf cart battery.
will claim more cycles
than others in these group sizes but none compete directly with a GC2 in terms of cycle life. Cycle life data across brands needs to be ignored. There is no standard for rating batteries for cycle life so best to use data across a single
You are not just buying Ah capacity
you are buying cycle life
& expected durability and longevity.
There are 12V golf cart batteries such as the Trojan T1275, and they do have the same cycle life as a 6V, but they are also taller, like the 6V, and a built to use the same plates thickness as a GC2 battery. These are not your typical 4D, 8D, Group 31, 27 or 24 battery. Group 4D, 8D, 24, 27 & 31 batteries simply do not have the plate thickness a GC2 battery does with very few exceptions.
Deka/East Penn is perhaps the largest private labeler of marine batteries in the US, the NAPA GEL you linked to is an East Penn GEL battery (1000 lab rated rated cycles)..
There are more re-branded East Penn batteries out there than any other I see. One example the Deka / Sea Volt / West Marine line. In that line up you have starting
, dual purpose
and deep cycle
G-24, 27 & 31 12V batteries which all share the same case. They simply do not offer a deep cycle 4D or 8D other than GEL, because it does not exist in the East Penn line up...
However, the G 24, 27 & 31 are only really deep cycle
when compared to the starting or dual purpose batteries with which share the identical case. They are not deep cycle
when compared to the GC2 or other true deep cycle batteries..
Here's the data across the Deka / East Penn / West Marine line up:
Flooded Batteries - Group 24, 27, 31 & 6V GC2
12V Starting - Cycles to 50% = Not Rated
12V Dual Purpose - Cycles to 50% = 200 (*4D & 8D flooded)
12V Deep Cycle - Cycles to 50% = 350
6V Golf Cart - Cycles to 50% = 700-1000
The above are LAB RATED cycles. Expect considerably less in the real world
As you can see the 12V "deep cycle" battery is only a "deep cycle" when compared to the starting or dual purpose batteries it shares a case with. If you absolutely must buy a 12V Group 24, 27 or 31 buy the deep cycle
version. If you absolutely must buy a 4D or 8D buy GEL or Lifeline AGM otherwise find a way to fit GC2 6V batteries. In many cases a 12V deep cycle is all that will fit. It is easy to see from the raw manufacturer data that these are NOT deep cycle
when compared to a real
deep cycle battery.
The only ones that have lab rated cycles for flooded 12V batteries the same or close, to their own brands 6V batteries, are Lifeline and the US Battery DCXC 12V series (at least those are the claims). In the real world I see US Batteries 6V GC2's outlast the 12V DCXC by a fair margin pretty consistently...
I know of no other brand, other than those listed above, that will rate their 4D, 8D, G-24, G-27 or G-31 flooded batteries at even half the cycles of their GC2 6V batteries.
The Deka / East Penn / WM product in 4D, 8D, 24,27 & 31 is less than half the rated cycles as their own 6V GC2 and these are by far the most popular marine batteries out there....
Don't just buy on Ah's buy on expected cycle life and buy a battery physically designed and intended for deep cycling not an imposter just labeled
as a "deep cycle".......