When combining multiple batteries, the best practice is to parallel each battery (with similar length conductors) to a busbar.
When outside of conduit, a cost-effective solution is the Victron "Power-In"
or its fused cousin, the Victron "Lynx".
Fortress eFlex and eVault original + MAX series batteries have internal fuses, so external fuses are not required.
For a clean look, inside of conduit, it is often convenient to purchase a busbar with the right amperage and stud rating.
Be sure to get two busbars - one for positive and the other for negative!
We commonly recommend an 8"x8" trough underneath the inverter, with the following busbars contained within:
Note: inverter and battery recommendations should be made in compliance with NEC.
You may need to add terminal fuse blocks
to regulate maximum busbar ampacity or to meet short circuit current interrupt ratings.