People who know about battery power on a boat will tell you the pinnacle of performace is floating the battery charge as often as possible. Often this advice comes from an armchair. It is easy in a marina with shore power but it takes a lot of generated power. For me, for example, everytime the vessel is under main engine, the opportunity to achieve float is immediately afterwards. The alternator is 63Ah, which is twice as much as the Victron charger from the generator.
For AGM batteries, the charging process is: bulk charging starts at current battery charge state and goes until about 26.5v, absorption goes from 26.5v to 28.4v or so and then the elusive float is when this number suddenly diminishes to around 26.5v. When you switch off the charging, the operating voltage will fall to around 25.6v. The result is 26v is generally considered to be fully charged for AGMs. Most good deep discharge AGMs can go down to 80% depth of discharge (DOD), which is 22 volts. I would not do this. The furtherest DOD I go to is 90%, 24v, which many unusefully consider to be 50% discharged (NOT DOD). Even that is low for me, because the big power consumers of battery power in boats are refrigeration and freezers, which are not always very efficient, and that suddenly takes the volts down below 23.5v, not even considering bilge pumps. I try to maintain a charge of 95 per cent.
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