Why does the power register return values around 16384 when the battery is idle?

The SAX Power Home applies a fixed offset of 16384 to the raw value at register 47. Subtract 16384 from the raw reading to obtain the actual storage power in watts. Positive results indicate discharge; negative results indicate charging.

No values appear even though the gateway connects. What should I check?

Confirm the Modbus unit ID is set to 64 (decimal), not the default of 1. The SAX battery uses unit ID 0x40 (64 decimal). A wrong unit ID produces silent timeouts. Also verify the device is reachable on port 502 from the same network segment.

Values are erratic or all registers return errors after a firmware update.

SAX has two Modbus modes in later firmware: Mode 1 (native register table, used by this template) and Mode 2 (SunSpec-aligned). If the device was reconfigured to Mode 2, the register addresses for SOC and power will shift. Confirm Mode 1 is active in the device communication settings.

Is it safe to write to the batterymode register during normal operation?

Use caution. Register 43 controls the discharge power limit. Writing 0 blocks discharge immediately, which can affect household self-consumption and may interact with the battery's own protection logic. Always restore the original value after an automation sequence, and do not write values exceeding the unit's rated power. Incorrect setpoints can void warranty support.

Free Modbus template: SAX SAX Power Home (Plus) (battery)

The SAX Power Home (Plus) is a residential AC-coupled battery storage system with an integrated inverter function, eliminating the need for a separate hybrid inverter. It uses LiFePO4 cells and connects to the grid as a single-phase AC unit. This Modbus TCP template reads battery state of charge and instantaneous storage power from the SAX Power Home (Plus), and writes the discharge power limit via the batterymode register. Connecting via the ModbusCloud Gateway gives installers and building owners live battery data and remote mode control in one place.

Name	Address	Function	Type	Unit	Access
power Instantaneous battery power; raw value requires offset of 16384.	47	FC03	uint16	W	R
soc Battery state of charge in percent, 0 to 100.	46	FC03	uint16	%	R
batterymode Discharge power limit setpoint; write 0 to block discharge.	43	FC16	uint16	W	W