What does ‘battery communication lost’ on an inverter mean, and how do you fix it with a rack battery?

Direct answer: The alarm means the inverter is not receiving data from the battery’s BMS over the communication link, so it may fall back to voltage-only control or stop charging and discharging. The battery itself is usually fine. Check, in order: the right port and cable, the cable pinout, the protocol selected on the inverter, the battery’s address or DIP switch setting, termination if required, and firmware. Change one thing at a time and record what you changed.

What the battery offers. Redway lists RS485, RS232 and CAN-bus with a manual DIP switch on the PM-LV51100-3U-PRO and PM-LV48100-3U-PRO, and RS485 and CAN bus on the PM-LV51200-5U. Each page lists compatible inverter brands, but a brand on the list does not mean every model or firmware version works. Check the inverter maker’s battery compatibility list for your model.

Port and cable. Many rack batteries have separate ports for CAN, RS485 and battery-to-battery links that use the same RJ45 connector. A cable in the wrong port, or a straight network cable where the inverter needs a custom pinout, gives no data. Compare both manuals’ pin assignments and make or buy the cable to match. Our post on connecting a PM-LV battery to a hybrid inverter covers the first setup in more detail.

Protocol and address. The inverter must be set to the battery brand or protocol the battery uses, and the master battery must have the address the inverter expects. In a parallel bank only the master normally talks to the inverter, and the others are addressed by DIP switch. A wrong DIP setting after adding a module is a common cause of a lost link.

Termination and noise. Long or unshielded communication cables run beside DC power cables can pick up noise. Keep them short, separated from power cables where possible, and use termination only if a manual calls for it. Re-seat connectors and look for bent pins.

When it still fails. Note the inverter model and firmware, battery model and firmware, cable details and DIP settings, then contact both suppliers. Do not run a lithium bank long term on an inverter that cannot read the BMS unless both makers confirm the settings, because charge limits then depend on voltage settings alone.