Is it damaging to my lithium batteries to keep the boat connected to Shore power for extended periods of time? Or is it better to let solar power take over. We only leave bilge pumps on and one refrigerator.
I’m no expert but my personal preference would be to leave the boat on solar - but it depends a little on how much solar you have and how predictable the sunshine is where you are. With one fridge (plus background draw) I would think you would have a few days reserve power to cope with cloudy spells. This will allow a cycle each day as power is used over-night and replaced by the solar during the day.
I have certainly seen discussions about keeping LiFePO4 batteries at 100% all the time not being good for them - but how “bad” it is is often unclear. I have seen many references that advocate only charging to 80 or 90% but again whether that is based on science of hearsay is hard to ascertain.
Whether the battery/BMS manufacturers have already made these allowances is also something to consider. Looking at my Victron BMS its “charged voltage” is set at 28v (with 8 cells) that’s 3.5v/cell. Fully charged is often regarded as 3.65v/cell. So on my Victron system it does seem there is already some inbuilt headroom.
Another thing you could consider is reducing the fully charged voltage on your battery charger.
The vast majority of active cruising blue-water boats with Lithium probably ignore it and just leave the charge controller to do its thing and will get to 100% every day - but for us there are many days where that does not occur.
In my opinion it would be much much worse to get into a situation where the batteries fully discharged - that can definitely cause damage.
One conversation I have never had on the dock is “I left my batteries on charge and now they are dead…”