Register 302 returns a value that is off by one address. Why?

FEMS Modbus tools default to a base address of 1, which shifts all register addresses by one position. Ensure your Modbus client and the ModbusCloud Gateway use a base address of 0. With base address 0, register 302 correctly returns the battery state of charge.

The Gateway connects but register 415 always reads zero or stale data.

Register 415 reports discharge power and returns zero when the battery is idle or actively charging. Negative float32 values indicate charging. Confirm the battery is in an active charge or discharge cycle before concluding there is a communication problem.

No values appear at all after importing the template. What should I check?

The ModbusCloud Gateway must be on the same physical network as the FEMS unit and able to reach its IP address directly. Firewalls or VLANs that block TCP port 502 will prevent all register reads. Verify network routing and confirm no firewall rule is blocking Modbus traffic on that port.

The power register uses float32. What does that mean for reading two registers?

A float32 value spans two consecutive 16-bit Modbus registers. Function code 4 must request two registers starting at address 415. If your client requests only one register, the returned value will be incomplete and appear as garbage. Ensure the data type is set to float32 in your Modbus client configuration.

Free Modbus template: FENECON Modbus-API (battery)

The FENECON Modbus-API is the built-in Modbus TCP interface of FENECON energy storage systems, powered by the FEMS energy management software. It exposes aggregated system channels over a local Ethernet connection, making battery data available to external controllers, building management systems, and monitoring platforms without additional hardware. This template reads the two core battery registers: discharge power at address 415 and state of charge at address 302. Connecting the ModbusCloud Gateway to the same LAN as the FEMS gives you continuous visibility into battery behaviour across one or more FENECON installations.

Name	Address	Function	Type	Unit	Access
power Battery discharge power in watts; negative values indicate charging.	415	FC04	float32	W	R
soc Battery state of charge as a percentage, 0 to 100.	302	FC04	uint16	%	R

FENECON Modbus-API (battery)

Overview

Use cases

Installation

Things to watch for

Registers (2)

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