Why do power_a and power_b always read zero?

Both registers are only populated when the battery is actively charging or discharging. If the inverter is in standby or the battery is at full charge with no load, both registers legitimately report zero. Confirm the battery is cycling and that the RS485 unit ID in the portal matches the address configured on the inverter display.

The Gateway connects but soc never updates. What is wrong?

The most common cause is a mismatch in baud rate or parity. The Growatt Hybrid Inverter uses 9600 bps, 8 data bits, no parity, and 1 stop bit. Verify these settings on the inverter and in the portal configuration. Also ensure the RS485 cable polarity (A+/B-) is not reversed between the inverter terminal and the Gateway.

I get intermittent timeouts on the RS485 bus. How do I fix this?

Growatt RTU firmware requires a minimum inter-command gap of 850 ms. If the Gateway polls too aggressively or shares the bus with another master, collisions cause timeouts. Set the poll interval to at least 1 second, add 120-ohm termination resistors at both ends of the cable run, and confirm no other device shares the same unit ID.

Is it safe to write to batterymode_a and batterymode_b remotely?

Use caution. Writing an unsupported mode value or switching modes during active charging can interrupt mid-cycle battery management and may affect system behaviour in ways not covered by warranty. Always test mode changes during low-load periods, confirm the intended mode is active on the inverter display afterward, and document each write in your maintenance log.

Free Modbus template: Growatt Hybrid Inverter (battery)

The Growatt Hybrid Inverter is a grid-tied hybrid PV inverter with integrated battery storage management, used in residential and small commercial solar-plus-storage systems. This Modbus RTU template reads battery power (power_a, power_b), battery state of charge, and cumulative energy throughput from the inverter over an RS485 connection. Two writable battery mode registers (batterymode_a, batterymode_b) allow remote switching between operating modes such as Grid First, Battery First, and Load First. The template gives installers and building owners live battery visibility and mode control from a single ModbusCloud Gateway.

Name	Address	Function	Type	Unit	Access
power_a Battery charge or discharge power, first measurement word.	1009	FC04	uint32	W	R
power_b Battery charge or discharge power, second measurement word.	1011	FC04	uint32	W	R
energy Cumulative battery energy throughput, charge or discharge.	1054	FC04	uint32	Wh	R
soc Battery state of charge, 0 to 100 percent.	1014	FC04	uint16	%	R
batterymode_a Battery operating mode setpoint, primary control register.	1102	FC16	uint16		W
batterymode_b Battery operating mode setpoint, secondary control register.	1092	FC16	uint16		W