Mark,
Thank you for the feedback. Appreciate you taking the time.
You are correct in that the “power station” would effectively be an additional - independent house bank. I also agree it is a leap from my current propane system which, like yours, consumes a bottle a year - at most. I singlehand almost exclusively so that reduces gas consumption even further. I agree this reconfig would expose me to some risk in terms of “range” (to steal a term from the EV world).
I’ll try to make my case…or unmake it.
I am calling this new power source a “power station” to differentiate it from a “battery” because these new devices are equipped with a layer of functionality including MPPT solar controller, 110 VAC inverter, monitoring apps (in many cases), easy portability and onboard BMS. So there are benefits associated with this approach which have some value beyond that of a POB (plain old battery). The power station I am considering weighs 30 Lbs and is rated 1500 watt hours. Maybe 1200 WH usable.
As a result of some of my racing activities I have a fairly well refined power budget for the boat and, as you point out, charging requirements are key. Having said that, I have a good handle on what goes where with regard to onboard power consumption.
There are definitely challenges. I currently have a Kidd Midnight controller and two one hundred watt panels. The panels are adequate to keep the boat fully charged for about 8 months a year (sun angle and weather). I occasionally have to use engine charging in winter months, usually 45 minutes to an hour a day due to cooler box AND diesel heater loads primarily. I also run some instruments to keep an eye on depth, wind speed, anchor alarm. I have a serpentine driven 130 amp alternator (tuned down to 75 amps for the time being).
Offshore, I require daily engine charging due to AP demand, but my most frequent use case are long motoring sessions followed by racing/sailing followed by more motoring. This is due to my location upriver on the California Delta and the need to motor 10 NM out of a tight river system near my home and then out of the Delta into SF Bay. another 25 NM. I just love the Delta and motoring slowly though it is something I enjoy so I consider these parts of the trip part of the experience not a hassle driven by charging batteries.
I have sailed out of the Delta numerous times but with narrow channels, adverse currents, and depth constraints, motoring is less stressful and a lot faster trip to open sailing ground in SF Bay.
The plan regarding charging the power station is as follows. At the dock, plugged into shore power I would use pass through charging. All cooking gear can be used at the output of the station which it is simultaneously being charged via shore power, similar to an UPS system. I would be using the integrated power station inverter to give me 110 VAC for cooking. We then leave the dock with a full station battery. The drain on the station is essentially zero when not cooking or using 110VAC for other purposes which would be rare. Meanwhile the bank is being charged by batt charger at the dock and alternator/panels underway.
So now I need to cook (heat water, food, whatever). I fire up my induction cooktop boil some water for coffee, down 100 watts (I have tested). Fire up the air fryer and the induction cooktop for dinner and use another 600 watts (air fryer consumption tested). Total power for dinner and morining coffee + miscellaneous, let’s say 800 watt hours per day. At 12 volts I need to find 58 amp hours a day to recover. During summer I top up my batteries by about noon on the panels and that is using my 12VDC cooler for a freezer. The loads are then carried by the panels and I shunt about 10 amps out of the panels The Kidd controller has a special “load” output which can automatically redirect unused SA power to a load which, in this case, would be the power station. So that would give me about four ish hours at 10 amps while at anchor. when sailing with all my gear turned on and the AP engaged I may get just a few amps. So at anchor I loose ground slowly, say 320 watts per day on the power station (or 25% per day).
The house bank is fully charged daily by the SAs. This sounds pretty good. When sailing long distances offshore we are back to engine charging which I had to do anyway. In this case I might see as much as 20 amps of charge current to the station the SA panels + the Cig lighter input. I also have the option of adding one or two lightweight 100W flex panels to the system while at anchor. I currently have one 100 watt flexible panel which is not used aboard except for long distance racing when it is attached to the existing SA wiring harness and attached to my dodger roof (my two framed panels hang on the pushpit). The flex panels are flat and easy to store under a bunk so I could simply whip that out and deploy in the cockpit for some additional oomph.
The station cig plug charging input maxes out at 10 amps. I would hard wire this from house bank to a breaker and then to the station. Typically this charge source would be activated via the breaker only when we are motoring. So we can tap some power from the alternator this way without a lot of complex switching, just need to remember to manage the breaker. We now have another 120 watts per hour when the engine is running for a total of 240 watts/hr. Since I usually get engine charging done in an hour, we only get the 240 for one hour and that is the one scenario where getting charge directly from the alternator would be very useful. I need to research the availability of a splitter or some such so I could SAFELY maintain max alternator output through the charging cycle and simply redirect excess amps to the station. As my AGMs charge my regulator follows its charge cycle algorithm and begins to reduce charging voltage/current accordingly so in the latter part of the bank charge cycle there are tons of amps available to the station if I could figure out how to get them there.
On balance I think I can manage the charging part of the equation.
Now on to other Pros and Cons I have come up with
Pro
1500 watt station inverter now available for whatever at dock and underway
No propane on the boat - plumbing/tanks/electrical maint. gone
Removes the stove. The oven part has never been reliable and it is heavier that batt which replaces it
Current marine stove alcove big enough and low enough for unobtrusive battery install and added storage
Power station management app
Low install complexity and easy portability for other uses - on my boat there is an 110 shore power electrical socket just above the galley stove. I will permanently plug into this socket for shore power pass through charging when shore power available. Easily unplugged for portability
Cost of stations is dropping as China economy tanks 
Con
Added charging complexity and range risk - mitigation power budget and supporting design
Risk associated with high voltage 110 VAC underway - mitigation, be careful its dangerous
System failure is going to be hard to deal with - mitigation, bring aboard a jetboil and store small camp bottle in propane locker, ditch this after adequate experience but save the original infrastructure bits. If I screwed up I can go back to propane.
may be unable to safely split alt output between bank and station. mitigation - research availability of splitter
May be an issue leaving unit on long term charge, will have to remember to charge station prior to passage. mitigation - I do power my cooler up a day before departure to get it and contents down to well below freezing on shore power. I would add station charging to my pre depart checklist.
