The short answer
Shut it down to stop further discharge, see if the inverter can force-charge, measure voltage and contact BYD service.
Plain explanation
From the BYD manual for the Battery-Box Premium HVS/HVM: Shut the battery down – avoid further discharge. Check whether the inverter can force-charge. The rest of the checklist is below; work through it in order. This is a warranty/support case: note the code, time and serial number before calling the manufacturer.
Steps from the source
- Shut the battery down – avoid further discharge
- Check whether the inverter can force-charge
- Installer measures voltage; cell <1.5 V = undervoltage
- Contact BYD service with the checklist
Source
BYD Battery-Box Premium HVS/HVM Service Guideline & Checklist (BCU2.0) V1.1, 2025-08-08, §2.9 EC110 + §2.10www.bydbatterybox.com ↗
Where installers ask this
- SMA STP10.0 SE + 2x BYD HVS Notbeladung (r/DeutschePhotovoltaik)
- reddit.com/r/DeutschePhotovoltaik/comments/1iwwnn6/
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.