Hey stue...yeah they're supposed to be good reserve batteries but i was looking more for a dual purpose AGM with a crank rating. Some of them are terrific as just a reserve but wanted a true back up start battery, that will be used as a reserve most of the time.
Pretty sure those fullriver ones are just reserve types, the one i was looking at seriously was the same as johncar up there ^^, century agm coz is an actual dual purpose and maybe 500ish CCA. The other issue is still clearance...they say 215mm to top of terminal but thats screwed down fla without cable on, plus also tray, plus rubber/mount...adds up fast in height.
The optima bluetop i have is about 195mm from memory and that only just makes it...tis why i figure i'm in strife getting one of these upright on the other side with same clearance constraint.
The other batt i was looking at was an odyssey pc1350 coz its about the only dual purpose agm the right size with a low profile...but its a massive big mother of a thing and wayy overkill.
Only need 500CCA tops (fair bit less in reality) to start a 70 4 stk, but i can chew thru 50-60 A on an aux for a decent nights fishing meaning i need at least 80+AHr reserve capacity for longevity, so a 100Ahr seemed about right. Short distance/trips from ramp to fishing so charging the aux whilst out there isnt something i factor in. Could maybe get away with a 85-90 but found even then they're about the same height so pointless and crap as a backup crank.

If i knew ones like the fullriver/remco/ritar type chinese agm's could be a good backup crank battery then maybe they;d be good enough instead of a dual purpose type like the century/lifeline/odyssey/deka types.

If Andy pops back he might be able to help there.
Gotta go out for a bit, tx for the help and talk later.