Siemens Junelight Smart Battery (battery)
The Siemens Junelight Smart Battery is a residential lithium-ion energy storage system designed to maximize self-consumption from rooftop solar installations. This ModbusCloud template connects to the Junelight via Modbus TCP and reads the two core operational registers: instantaneous battery power and state of charge. Power sign indicates charge or discharge direction. Together, these two values give installers and building owners the real-time visibility needed to track storage behavior, detect anomalies, and feed data into portfolio dashboards across multiple residential sites.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 2, read only
- Brand
- Siemens
- Last updated
Registers (2)
2 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| power | W | Read | |||
| soc | % | Read |
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Use cases
- Monitor instantaneous battery power to verify the Junelight is charging during midday solar surplus hours.
- Track state of charge over the day to confirm the battery reaches full capacity before evening peak demand.
- Alert on state of charge dropping below a threshold to detect unexpected overnight discharge or standby losses.
- Compare daily charge and discharge cycles across multiple Junelight sites to identify underperforming installations.
- Report battery power direction to verify the system switches from charging to discharging when grid import occurs.
Installation
Request Modbus TCP activation for your Junelight unit from Siemens or your installer, as the interface must be enabled on the device before any register access is possible.
Connect the Junelight to your local Ethernet network and note its IP address; confirm port 502 is reachable from the network segment where the ModbusCloud Gateway will be placed.
In the ModbusCloud portal, add a new gateway, import the Siemens Junelight Smart Battery template, and set the unit ID to 1, which is the default Modbus slave address for this device.
After saving, open the live register view and spot-check the soc register at address 8: the value should match the charge level shown on the Junelight's front-panel display.
Things to watch for
Why does the gateway return a connection error on port 502?
Modbus TCP on the Junelight is not enabled by default. You must contact Siemens support or your certified installer to activate the Modbus interface on the device. Once activated, confirm the Junelight's IP address is reachable and that no firewall blocks port 502 on your local network.
The soc reads a large unexpected integer value. What is wrong?
The soc register is a 32-bit signed integer spanning two consecutive 16-bit holding registers. If your client reads only one 16-bit word, the value will be incorrect. Ensure your Modbus client reads two registers starting at address 8 and decodes them as a single int32 in big-endian order.
Power register shows zero even though the battery is active. Why?
Address 6 for the power register also occupies two 16-bit holding registers. Verify you are reading two registers (addresses 6 and 7) and decoding as int32. A reading of zero can also indicate the Modbus session has timed out; check your gateway polling interval and TCP keepalive settings.
Values appear briefly then the connection drops repeatedly. What now?
The Junelight Modbus TCP server may close idle connections after a short timeout. Set the ModbusCloud Gateway polling interval to no longer than 10 seconds and ensure TCP reconnect is enabled in the gateway settings. Persistent drops can also indicate an IP address conflict; assign a static IP to the Junelight.
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