DELTA 3 Plus + 48V Rack Battery Success
Finally got my EcoFlow DELTA 3 Plus working with a third-party 48V server rack LiFePO₄ battery using an expansion adapter.
Initially, I kept getting Short Circuit Protection (4) every time I energized the external battery and thought something was wired wrong.
Turns out the issue was simply that the DELTA was nearly full while the external battery was much lower. Once I got them to a similar state of charge, everything connected immediately.
Now the DELTA recognizes the battery and is charging/discharging it normally.
Pretty impressed with the flexibility this opens up. Instead of buying a proprietary expansion battery, it looks like standard 48V rack batteries are a viable option if you use the correct adapter and match the battery voltages before connecting.