All power channel registers read zero even in sunlight. Why?

Check RS485 wiring polarity first: A+ must connect to pin 1 and B- to pin 2 on the Jupiter C Plus RS485 socket. A reversed connection returns no data. Also confirm the unit is powered on and actively charging or discharging, as the device may suppress output during standby.

The SOC register reads an implausible value. What is wrong?

The soc register is uint16 with no scaling factor defined in the template. The raw register value should equal the percentage directly. If the value exceeds 100, suspect a unit ID mismatch: you may be polling the wrong device on the bus. Confirm the Modbus slave address set on the Jupiter C Plus matches the unit ID in the portal.

Only some MPPT channels show data. Others are stuck at zero.

The Jupiter C Plus has four physical MPPT inputs (PV1 to PV4). If fewer than four panels are connected, unused MPPT channels will legitimately report zero. Cross-check how many panels are physically wired to the unit before treating a zero reading as a fault.

The Gateway connects but register reads time out intermittently.

The Jupiter C Plus RS485 interface does not supply power to external adapters on the Jupiter C Plus variant (pin 3 is inactive). Ensure the RS485-to-serial adapter has its own power supply. Also note that only one Modbus master can communicate at a time: if another device (such as a Home Assistant integration) is polling simultaneously, requests will collide and cause timeouts.

Free Modbus template: Marstek Jupiter C Plus Battery Storage (battery)

The Marstek Jupiter C Plus is an all-in-one balcony battery storage system with an integrated microinverter, designed for plug-and-play solar self-consumption in residential and small commercial settings. This Modbus RTU template reads battery state of charge and per-channel MPPT power across five input registers (power_a through power_e), giving you live visibility into each solar input string and overall storage level. Connecting the ModbusCloud Gateway to the Jupiter C Plus RS485 port lets you log, trend, and alert on battery and PV data without relying on the Marstek cloud app.

Name	Address	Function	Type	Access
soc Battery state of charge, 0 to 100 percent.	16	FC03	uint16	R
power_a Instantaneous power reading from MPPT channel A.	13	FC03	uint16	R
power_b Instantaneous power reading from MPPT channel B.	3	FC03	uint16	R
power_c Instantaneous power reading from MPPT channel C.	6	FC03	uint16	R
power_d Instantaneous power reading from MPPT channel D.	9	FC03	uint16	R
power_e Instantaneous power reading from MPPT channel E.	12	FC03	uint16	R