There is no "by far" unless you are comparing GC-2's with group 27 hybrid marine batteries. The disclaimer of "if one of them goes out" doesn't really seem to happen and if you have 4 or more, then it's a mute point.
Here's the math
Using the
min@25A rating;
2 6V T-105's; 447 min / 122 lbs = 3.66 min/lb
1 12V T-1275: 280 mi / 82 lbs = 3.41 min/lb
Using the
20 hour Ah rating
2 6V T-105's; 225 Ah / 122 lbs - 1.84 Ah/lb
1 12V T-105; 150 Ah / 82 lbs = 1.82 Ah/lb
I will agree that if you are only using 2 batteries, it's more of a personal choice between 225 Ah @ 124 lbs or 300 Ah @ 164 lbs. If you are using 4 or more, the advantages of 6V become more prevalent. If you go to the
Lifeline website and look at their
min@8A rate, there is even more separation between the advantage of 6V over 12V. Trojan does not give this rating in their chart.