External BMS recommended for LFP 12v or 24v batteries in series?

[Skid]

I am within 2 months of ordering what I need for a whole house system using max 5kwh per day. I have received a lot of good advice so far and because of the lack of hardware and reasonable shipping I'm going for preassembled batteries either through Xuba or through Amy at Shenzhen Luyuan. Before I order I'd like all my ducks in a row to ease communication with Chinese vendors.
I'm looking for batteries of 50# more or less to lessen the chances of damages when handled in this 'third world' country, so looking at 4 12v 200ah or 2 24v 100ah batteries in series for 48v, more later if it's not enough to get me through bad weather for a couple days. Two back to back hurricanes a couple months ago gave me a serious reality check.
My concern is BMS for multiple batteries in series. Is there a way to make the internals play nice or is an external BMS preferred, and if so will it complement the existing internal BMS or do they need to be disabled? Does an external simply mount externally?
Obviously I'm not an engineer. My profession was a ship's navigator which is no help at all here.

 

[snoobler]

If freezing temperatures are a concern, make sure you get batteries that have low temperature protection built in.

I am not aware of a BMS system that operates as you describe. One would NEVER want to disable a battery's own BMS because it is monitoring CELLS. To attach an external BMS to the cells, you would have to open the battery.

If you buy properly matched batteries (same manufacturer/capacity) and parallel charge them as 12V before assembling them, they should be good. For reference, Battleborn indicates you should notify them if you are planning to wire them in series, and they will MATCH them with the same capacity. Otherwise, you will just get batteries that meet the minimum specification. They also recommend the parallel 12V balancing about once per year.

I have a 4S2P 48V bank of Trojan T-1275 12V batteries, and due to known issues with them, I use the following:

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The balancers are connected in series and then one is connected to each 12V battery. They look for voltage differences between batteries and TRANSFER charge from the higher voltage batteries to the lower voltage batteries.