RE:  based on a rated 90-110 Ah reserve capacity on a Gr 41 battery.

Based on the usual rating of batteries the Group 41 is about a 55 or 60 AH
battery.  But such ratings are really muddled by the vendors especially for
starting batteries, whole bunch of mixed terminology.  But for figuring the
Group 41 for use as an aux battery the 55AH figure is used for comparison to
deep cycle and AGM batteries normally used for other than starting purposes
where a heavy load (like starting) is not a primary criteria.