how to get the last out of old/preserve new batteries.. and second hand upgrades

[PeppermintButler]

Hi all, I hope you are well

This is the 1st time I have ever created or even posted on a thread. so i am probably in the wrong place or doing something wrong haha. if this is already a well discussed topic I couldn't find it so i apologise for that if that's the case.

I have inherited a dying solar system and have decided to limp forward by purchasing a similar secondhand system.
I am trying to preserve the "new" battery system so i don't find myself in this situation next year.

OLD: 24v solar array > PL60 solar charger > 3kw latronics inverter > 4 x (energystore 6rp1080nx) batteries

"NEW": midnight classic 150 > 4kw latronics inverter > 4 x (energystore 6rp1080nx) batteries +(35amp battery charger, HRC fuse and additional bit and pieces including conduit and wiring for batteries and inverter)

I am wondering whether i can:

charge both battery banks with one solar panel array.(but still use them separately) use the old batteries to run fridge/pump(3kw inverter) new batteries to run everything else(4kw inverter) or some how automatically switch between the 2 banks at a set voltage
or
would I be better off setting up another solar array for cheap seeing as I have 2 whole system atm
or
float charge new bank from old bank and use them like a generator when the old ones die out until they completely die

and in the meantime apparently my new charger can switch between float charging 3 battery banks can i connect both battery banks to the neg- of the charger and pos+ to the different outputs of the charger.. just don't know if i can have a common neg-

sorry for the text dump just trying to give you all the info and pre-empt questions

thank you in advance for entertaining my crazy

p.s also interested in victrons battery protect BP-220 to cut off the batteries at a set voltage to make the solar usage idiot proof

 

[rodrick]

Old fla and new fla batteries don’t play well together you will trash the new batteries if you can do separate systems that would be my choice as far as a common ground I think you would be ok maybe someone with a midnight unit will chime in

 

[PeppermintButler]

Old fla and new fla batteries don’t play well together you will trash the new batteries if you can do separate systems that would be my choice as far as a common ground I think you would be ok maybe someone with a midnight unit will chime in

awesome, yeah thats why im trying to figure out "fancy" ways to get around connecting them.. but yeah new panels is probably the smartest