BYD Battery-Box shows EC103. What does the DIP switch or terminal resistor have to do with it?

Plain explanation

From the BYD manual for the Battery-Box Premium HVS/HVM: Read the code from LED flashes. Installer checks DIP switch (BCU1) or terminal resistor (BCU2). The rest of the checklist is below; work through it in order. Installer only: DC and AC work on a live PV system is dangerous, so owners should note the code and call their installer.

Steps from the source

1. Read the code from LED flashes
2. Installer checks DIP switch (BCU1) or terminal resistor (BCU2)
3. Remove the topmost module as described if needed
4. Restart in defined order

Source

Where installers ask this

• SMA Wechselrichter mit BYD-Batterie (terminal resistor) (r/DeutschePhotovoltaik)
• reddit.com/r/DeutschePhotovoltaik/comments/1vjn81v/

General guidance based on the manufacturer's manual or the named source. Always follow the current manual for your exact model and your national code. DC and AC electrical work is for qualified installers only. Not affiliated with or endorsed by any brand named; trademarks belong to their owners.