Why do I see NaN instead of values for some registers?

The SMA Data Manager returns NaN for registers whose source data is unavailable. Battery registers can return NaN at night if the connected inverter's CPU is powered only by PV and has shut down. Wait until the system is active or check whether the battery inverter is online in the Data Manager device overview.

The gateway connects but charge and discharge power both read zero. Why?

Registers 31393 and 31395 report charge and discharge as separate unsigned values, not a signed bidirectional value. If the battery is idle, both legitimately read zero. Confirm the battery is actively charging or discharging at the time of polling, then re-check the readings.

The Modbus connection drops every day or two. How do I fix this?

The SMA Data Manager Modbus TCP server can stop responding under sustained high-frequency polling. Increase your polling interval to at least 30 seconds per cycle. If the server freezes, it can be reset by disabling and re-enabling the Modbus server in the Data Manager web interface under the communication or Modbus section.

Values look correct but byte order seems wrong. What setting applies?

SMA uses Motorola Big Endian byte order: the high byte is transmitted first. Ensure your Modbus client is configured for Big Endian 32-bit and 64-bit register decoding. For the 64-bit energy register (31401), all four 16-bit words must be read in a single contiguous request; partial reads return inconsistent data.

Free Modbus template: SMA Data Manager (battery)

The SMA Data Manager (battery) is an energy management gateway that aggregates battery storage data from SMA PV systems over Modbus TCP. This template reads four system-level registers: charge power (31393), discharge power (31395), cumulative energy throughput (31401), and battery state of charge (30845). All values are exposed via the Data Manager's built-in Modbus TCP server under unit ID 2, which represents the system view. Connecting the ModbusCloud Gateway to the same LAN as the Data Manager gives installers and asset managers continuous visibility into battery charging cycles and storage utilisation without additional hardware.

Name	Address	Function	Type	Unit	Access
power_a Battery charge power, instantaneous watts drawn into storage.	31393	FC03	uint32	W	R
power_b Battery discharge power, instantaneous watts delivered from storage.	31395	FC03	uint32	W	R
energy Cumulative battery energy throughput, 64-bit counter value.	31401	FC03	uint64		R
soc Battery state of charge, 0 to 100 percent.	30845	FC03	uint32	%	R