Been reading this great site for a few years now.  So, long time, first time, here.

We started getting low DC voltage warnings whenever the inverter/charger was turned off, or shore power is disconnected.  We have 400 Ah of LFP batteries, 4 cells in series.  They are Winstons from China and are about 11 years old.  I have never disconnected them to charge cells separately, assuming that the House Power BMS would do keep them balanced.  The BMS did not show any faults when the low volts occurred.

I have not had a chance to check the cells individually, but I suspect one has gone bad.  I am not on the boat now so I still can't get there to do it.  I am reading, and reading, and reading, trying to complete a trade study on the options for replacing the batteries.  I have known that the Xantrex inverter/charger needs to be replaced since it is so old that it does not have a lithium charge profile available.  There is a custom setting, but you have to be a tech to unlock that feature.  We have always floated these batteries setting the charger to the lowest available float voltage.  The boat is docked in the Annapolis area, and we were living on it full time from 2019 until 2024, leaving the batteries floated all winter.  The temperature reading from the inverter was always much higher than ambient.  I think the batteries have yttrium chemistry and are supposed to be good for low temperature charging.

Anyway, all this is becoming a bit overwhelming.  I was a mechanical engineer, but this is out of my area.  I cannot afford to hire it out.  We do all our own work because we have to.

I've been reading about the over-voltage disconnect feature of most BMS's. 

Does the WattCycle 628 Ah model still have the disconnect problem?

Can I mix manufacturers?  Victron inverter, and and accessories with Battle Born, or other batteries?

Was considering the Victron NG batteries.  Our locker can fit 3 of those, for a total of 900 Ah.  Other manufacturers are about the same as far a space requirements.

Once I finish the design work, I can hire an electrical guy to review the schematic to provide advice.  I am willing to pay for that.

Contactors, or solid-state battery disconnects?

What manufacturers are reputable?  I am drawn to the Victron stuff.  I used all their MPPTs for our PV array we installed a couple years ago.

I feel like I'm going to be sitting here forever reading.