My Fox ESS battery shows 'BMS Lost' - is the battery broken?
Short answer
Not necessarily. 'BMS Lost' means the inverter has stopped hearing from the battery's management system, usually because a communication cable is loose, the battery is switched off or asleep, or a setting is wrong. Fox's manual (V1.0.8, checked 24 September 2026) tells installers to check the BMS cable. Charging pauses until communication returns.
Last checked 24 September 2026 · 1 source
What does this mean?
Homeowner: check the battery's external power switch/LED only. Installer: CAN cable, DIP switches, BMS firmware. 'Bms Int Fault' points to pack-to-pack cabling or DIP switch position.
What should I do first?
Record the code and current battery state before changing settings. Follow only the owner-safe reset steps in the manual.
When do I need an engineer?
Use an installer or manufacturer support route if the fault returns, involves isolation or protection, or the manual does not give an owner reset.
What to do next
If the system is hot, smoking, damaged or making unusual electrical noises, move away from it and follow the manufacturer emergency guidance.
Sources
Last checked: 24 September 2026