I think the 1/3 reserve minutes capacity rating, is a mistake.
Most AGM batteries say 1/3 the amp hour rating at the 20 hour rate., not 1/3 the reserve minutes rating
33 amps max, for a 100Ah battery.
Most AGMS, but Odyssey, Northstar or Lifeline, recommend no more than 1/3 the Ah capacity, as a max initial charging rate.
A 100Amp hour 12v battery is group 27 or larger, 12.5 wide 9.25 tall 6.5 wide thereabouts. Deplete this to the point it needs a jumpstart and the alternator will feed it well over 33 amps, for some variable amount of time, its not like lead acid batteries after jumping are exploding melting or failing after an unintentional discharge to the point a jump is required.
I largely ignore reserve minutes ratings, as the battery would need to have been healthy and fully charged when 25 amps was applied to it, and the minimum voltage the vehicle would still operate on, is so variable and largely unknown until it quits. Some vehicles might have no issues at running with a battery only able to maintain 11.1 volts, others would give up long before depletion to that voltage level.
Keep in mind manufacturer charge recommendations are kind of the best one size fits all to reduce warranty returns in expected usage for those it is marketed towards.
My small Asian AGMs, when deeply cycled, have gotten 10 times the maximum recommended charge amperage initially, briefly, and usually double to triple the max rate till they reach absorption voltage of 14.7v. I've doubled the max recommended charge amperage when well depleted, for upto an hour and 15 minutes. They do not get excessively hot and I do not worry and still behave well. The fear is excessive heating
When shallowly cycled their max amperage rate is not even able to be held for long, I just hook them upto a 100 amp power supply limited to 14.7v and let them feed on as much as they want. its when they are well depleted I worry about them as they can accept high amperage for long enough to heat up excessively. I also worry when they are older and am more timid with what voltage I allow, or more precisely the time at higher voltages when well depleted.
I do not do long term float. I charge at a temperature adjusted absorption voltage till amps taper to 0.5% of capacity ( 20 hour rate) then disconnect.
When deeply cycled I insure they get at least a c/3 charge rate if not every time at least once every 7 deep cycles.
Shallow cycle duty, I don't really worry about the rate as they cant accept high amperage for long anyway.
