Fusing LiFePo4 batteries in series-parallel

I have a 24 volt system, using the SmartSolar MPPT 150/100 and Victron Energy 1200VA 24-Volt 120V AC Pure Sine Wave Inverter.
Currently I have two LiFePo4 12.8 volt/100 Ah batteries in series. I’m adding two more batteries and will connect them in series-parallel to output 24 volts, doubling my amp capacity.

My research on this battery configuration says that I need to add another fuse on the positive of one of the battery banks. (Do I need just the one fuse?)
I’m stuck figuring out the proper amperage of the fuse.

Do you have a phoenix or a multi compact? The manual has fuse and cabling requirements.
And fuse each battery up to their common bus bar.
Your choice depends on your cable size from the bank to the bus and if you build in redundancy like the what happens of one bank has a probelm scenario and you have to limp on one set for a while)

The inverter is a Phoenix.
Could you please tell me where the MPPT manual has the fuse and cabling requirements, I could not find that info.
I believe there should be a calculation that determines the size of the fuse to protect the batteries downstream.

The lithium batteries have infinite (almost) amperage. So could pretty much blow most fuses. The issue is if the fuse it too large for wiring to blow it.

The internal fuse size for the inverter is there. You van either match that or go slightly under depending on fuse tyoe and blow rate.

What fuse type do you have in mind? A midi fuse?