SoC, SoH, and voltage registers return implausible raw values. Why?

SunSpec Model 805 uses signed int16 scale factor registers. The raw uint16 reading must be multiplied by 10 raised to the power of the corresponding scale factor register (for example soc_sf, v_sf). If your client ignores scale factors, all measurements will appear as unscaled integers. Apply the scale factor before displaying or alerting on any measurement.

The gateway connects but stridx and modidx both read zero. What is wrong?

SunSpec indices are one-based, so a value of zero indicates the register is returning the SunSpec 'Not Implemented' sentinel (0x0000 for uint16). Confirm the battery device firmware supports Model 805 and that the model block is correctly populated. Some BMS implementations expose Model 805 only when a physical module is actively connected and reporting.

Cell voltage and temperature readings appear identical for max and min. Is this normal?

If all cells report the same voltage and temperature, the BMS may be aggregating rather than providing per-cell data. Verify that the firmware version on your battery device supports cell-level telemetry. Also check the cellvmaxcell and cellvmincell index registers: if both return the same cell number, only one cell is being reported.

The gateway cannot find the Model 805 block at the expected address. What should I check?

SunSpec devices may place Model 805 on a separate logical Modbus slave unit ID from Models 802 and 803 when the combined register count exceeds the 65,535-register Modbus limit. Check the device documentation for a secondary unit ID dedicated to module-level data, and update the unit ID in your ModbusCloud portal accordingly. The model block base address is not fixed and must be discovered via the SunSpec header scan.

Free Modbus template: SunSpec Model 805 — Lithium-Ion Module Model

Name: SunSpec Model 805 — Lithium-Ion Module Model
Brand: SunSpec
SKU: 18802a70-1181-448e-bf72-fa629805b59f

SunSpec Model 805 is the Lithium-Ion Module Model, a standardized Modbus TCP information model defined by the SunSpec Alliance for monitoring individual battery modules within a multi-module energy storage system. The template reads per-module state of charge, depth of discharge, state of health, cycle count, module voltage, and per-cell voltage and temperature extremes and averages. String and module index registers identify each module's position within a bank. For integrators commissioning lithium-ion storage, this template delivers the cell-level granularity needed to track degradation and cell imbalance over time.

Registers (28)

28 read / 0 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 805 for this model.	0	FC03	uint16		R
l Model block length in Modbus registers.	1	FC03	uint16		R
stridx One-based index of the string containing this module.	2	FC03	uint16		R
modidx One-based index of this module within its string.	3	FC03	uint16		R
ncell Total count of cells within this module.	4	FC03	uint16		R
soc Module state of charge, scaled percentage.	5	FC03	uint16	%	R
dod Module depth of discharge, scaled percentage.	6	FC03	uint16	%	R
soh Module state of health, scaled percentage.	7	FC03	uint16	%	R
ncyc Cumulative full charge-discharge cycle count for this module.	8	FC03	uint32	count	R
v Module terminal voltage, scaled volts.	10	FC03	uint16	V	R
cellvmax Highest cell voltage in this module, scaled volts.	11	FC03	uint16	V	R
cellvmaxcell Cell number reporting the highest voltage in this module.	12	FC03	uint16		R
cellvmin Lowest cell voltage in this module, scaled volts.	13	FC03	uint16	V	R
cellvmincell Cell number reporting the lowest voltage in this module.	14	FC03	uint16		R
cellvavg Average cell voltage across all cells in this module.	15	FC03	uint16	V	R
celltmpmax Highest cell temperature in this module, scaled degrees Celsius.	16	FC03	int16	°C	R
celltmpmaxcell Cell number reporting the highest temperature in this module.	17	FC03	uint16		R
celltmpmin Lowest cell temperature in this module, scaled degrees Celsius.	18	FC03	int16	°C	R
celltmpmincell Cell number reporting the lowest temperature in this module.	19	FC03	uint16		R
celltmpavg Average cell temperature across all cells in this module.	20	FC03	int16	°C	R
ncellbal Count of cells currently active in balancing within this module.	21	FC03	uint16		R
sn Module serial number string.	22	FC03	string		R
soc_sf Scale factor exponent applied to the SoC register.	38	FC03	int16		R
soh_sf Scale factor exponent applied to the SoH register.	39	FC03	int16		R
dod_sf Scale factor exponent applied to the DoD register.	40	FC03	int16		R
v_sf Scale factor exponent applied to module voltage register.	41	FC03	int16		R
cellv_sf Scale factor exponent applied to all cell voltage registers.	42	FC03	int16		R
tmp_sf Scale factor exponent applied to all cell temperature registers.	43	FC03	int16		R