In a perfect world the batteries would get full before the charger switches to float. The reality is NO ONE is willing to pay for that technology in a charger so they do the best they can with algorithms to try and achieve that. The Sterling ProCharge Ultra and ProMariner Pronautic P are the identical chargers and used the same algorithms.
The reason ProMariner does not understand is is likely because Charlie Sterling created the smart algorithm. These chargers use what I refer to as "adaptive learning" algorithms. This means they look at % of power supply, time it took to attain XX.XX volts, time it took current to fall etc. etc.. They use all these parameters to try and get your battery as full as possible BEFORE switching to float and they do a darn good job at it.. These chargers also revert back to absorption voltage every few days to keep the batteries healthy. They are one of the smartest chargers made.
Compare an algorithm like that to a "dumb" smart charger like those that use egg-timer based algorithms. Some of the chargers out there start a 4 hour "egg timer" when the charger has been switched on. Whether or not you even attained absorption voltage, on this particular brand of charger is irrelevant. It will simply go into float at 4 hours regardless of battery SOC. Talk about poor charging..
In order to do this based on current MULTIPLE shunts would need to be used. The charger has no idea what is a load, and what is going to the battery, so they simply can not use a single external current shunt as a measurement. To do current based charging, as opposed to voltage based, we would ideally need a loads shunt, a net current battery shunt and a charge shunt for other external sources such as solar. This would allow full cross checking to be sure what the charger was seeing was accurate. This would lead to MASSIVE wiring nightmares, heck folks can't even wire a single battery monitor shunt correctly, imagine three shunts! This is why every charger on the market, for marine use, is voltage based not current based.
Balmar was recently working on this type of charging for alternator regulation but put it on a far back burner when they likely realized the install level, liability and overall COST of the product when compared to just how effective the current regulators already are..
Many folks assume the old Link 2000's did this, but it is incorrect. The settings in the old Link 2000 were for the battery monitor portion though nearly every owner I talk to thinks they control the charging and that it goes to float when it sees 2% current. Nothing could be further from the truth and all charging is controlled inside the inverter charger and it still has a 4 hour max absorption override. I can point to many examples of Link 2000 controlled systems on large banks where it dropped into float at 4 hours regardless of whether or not the bank was truly full. The reason they do this is most like LIABILITY & cost.... Too many variables in owner or pro-level installs to rely on an external shut to control charging.
You have one of the best and smartest chargers out there. Focus on the myriad of other variables you CAN control.....
*Battery location/orientation - On sailboats this matters.
*Battery Temperature - Engine room = DUMB
*Average DOD - Shallow cycles equal longer life.
*100% Frequency - How often you get back to "full"?
*Temp Compensated Charging - Does your charger drop voltage above 80F? Does it boost voltages when below 70F?
*Charging Voltages - Are you getting to 14.8V?
*Float voltages (Trojan's really like 13.6 -13.8V)
*Periodic Absorption - Absorption boosts are healthy if batts left to sit
*Off season storage - The cooler the better, 100% disconnected.
*Equalize Before Lay Up - Wake up in the spring with a short one. *If cells are already in balance only push the 15.5V until current stops dropping. *Temp corrected of course.
*Equalization - Regular equalization, when necessary. This is normally at least bi-yearly. Proper absorption voltages lead to less need for equalization. Charging at 14.4V you may need four times per year but charging at 14.7 - 14.8V you may need only one or two per year. Even short periodic 30 minute equalizations help quite a bit.
*Proper bank wiring - How they are wired matters. Wire gauge matters, clean connections matter, low resistance connections/terminations matter.
*Electrolyte - Keep up with it or add a watering system
*Opening Cells Too Often - Avoid this DO NOT DO SG CHECKS CONSTANTLY! This only leads to increased potential for contamination. My customers who are chronic SG testers often have the shortest bank life due to cell level contamination. Keep battery tops SPOTLESS so when you do open them no crap falls in there. Contamination causes premature gassing. If cells don't all begin to gas at same voltage your most likely cause is contamination.
*SG Tester Storage - How are you storing your hydrometer & keeping it 100% clean?
*Commissioning Charge - Wire in parallel and push voltages to 15.5V for 12V or 7.75V for 6V for 30 minutes to one hour. I call this a wake-up charge & cell balance. Cell balance not important for parallel wired bank but can be helpful in series banks.
*Matched Bank - Matched for date codes and impedance measurements. Most any good battery shop will have an impedance tester (Midtronics etc.) ask them to test the batteries until you find a near perfectly matched set. I bring my own tester.
*Accurate Voltage Sensing - Inaccurate voltage sensing can lead to under charging.