I treat Maximum charge rates the same as maximum tow rates, lol. Just cos it states my 4x4 will tow 3 ton, does not mean I should or it is the optimum for vehicle life. It's my experience that some conservative use is a better approach. As "they" say, "All things in moderation." I guess my justification for my figures, is the life I'm getting from mine.
RR Can I clarify, are you saying your Noco charger pulses 15.8 V when charging an AGM? If so, my opinion, way too high, most smart chargers in Boost are set to 14.4 V, some at 14.5. Those kinds of voltage are usually only used in a Desulphation mode.
One of the reasons I use a DC-DC in my 4by, the alternator is often at 15 V, at least the Redarc lowers this to 14.5 in Boost/Absorption. Here are some differences in smart chargers
BTW Redarc BCDC1220 DC-DC - Boost = 14.5 V - Float = 13.3 V
Projecta Intellicharge IC Series 240 VAC charger - Boost = 14.4 V - Float = 13.8 V
Projecta IDC25 DC-DC + Solar - Boost = 14.4 V - Float = 13.7 V
Voltech BC-1230P 240 VAC Charger - Boost = 14.4 V - Float = 13.2 V
Victron MPPT 100/20 Solar Control - Boost = 14.4 V - Float = 13.8 V
CTEK D250S DC-DC + Solar - Boost = 14.7 V - Float = 13.6 V
+ many more
You can see the differences in voltages, I think the CTEK is a little high for Boost/Absorption voltage. The Redarc and Voltech are the better Float voltage as these voltages are where an AGM begins to gas off. At 13.8, they definitely will gas.....