As I hope you know, 400 amp/hrs of LifePo4 is nothing to fool around with - you can quickly and easily destroy them. this isn't really a question of "premium", I doubt your pro-mariner even has settings for your batteries. There are a lot of threads on this board about managing LifoPo4 batteries that are worth reading.
I am not a LifePo4 expert (nor have them) - hopefully someone will correct any errors in what follows:
- The hum from the Victron is normal - it's a transformer. And you're pushing it at its maximum rating when you go to 80amps so it hums louder. I have the bigger Multiplus that does 120 amps and it hums too when the charge rate is high.
- LifePo4 batteries don't really like to be at 100% charge. It doesn't hurt them at all to be at partial charge. As you approach 100% the voltage can go up very quickly destroying the battery. Many people use a BMS to cut off the charger when the voltage starts to go too high. Another tactic is to go to float at a voltage that's well below the
danger level. Or simply cut off charging then.
- How is your Multiplus set up for bulk, absorption, and float charge voltage? It should not be set up like your old batteries. Victron has settings for
Lithium. They also have a relay that can be connected to a BMS.
- Whatever is telling you charge percentage is likely wrong. These meters accumulate errors over time even with regular batteries. I'm not sure what happens with
Lithium. And the difference between 0 amps and 1-2 amps charging doesn't tell you anything. No load, resting voltage is what you care about.
- It is quite possible that your solar charger is confusing the Victron. And how is it setup? I would disconnect the solar controller while trying to figure out the Victron.
Again, read some of the great threads on this board.