The gateway connects but register 16 always returns zero. Why?

A persistent zero can indicate the battery is idle and neither charging nor discharging, which is valid. However, if zero persists during known solar production, verify that Modbus TCP has been fully activated by Siemens support. Some firmware versions require explicit enablement before the interface responds with live data.

I get a connection timeout every time the gateway polls. What should I check?

Confirm the Junelight's IP address is reachable from the ModbusCloud Gateway on port 502. Check that no local firewall or router rule blocks TCP port 502. Also verify the unit ID is set to 1 in the portal, as the battery does not respond to other unit IDs.

The power value looks correct in magnitude but has the wrong sign. Is this normal?

The power register is a signed int32. A negative value indicates the battery is discharging energy to the home or grid; a positive value indicates charging. If the sign appears inverted relative to your expectations, check whether your PV system inverter is the one changing direction, not the battery itself.

Why do I see large, implausible spikes in the power reading occasionally?

Transient spikes in a signed int32 register can occur if the two 16-bit words are read across a register boundary update. Ensure your polling interval is at least 5 seconds to reduce the chance of mid-update reads. If spikes persist, check network latency between the Gateway and the battery, as high latency can cause partial reads.

Free Modbus template: Siemens Junelight Smart Battery (pv)

Name: Siemens Junelight Smart Battery (pv)
Brand: Siemens
SKU: 1c8329fe-12ae-4961-b04e-42c17c3b9791

The Siemens Junelight Smart Battery is a residential lithium-ion battery storage system designed to maximise self-consumption from a connected photovoltaic installation. This Modbus TCP template reads the instantaneous battery power register, giving your ModbusCloud portal real-time visibility into whether the Junelight is charging or discharging and at what rate. Connecting this single register to historical trending and alerting lets installers and homeowners track battery behaviour over time without relying on the Siemens app alone.