All register values read as 0x8000 or 0xFFFF. What is wrong?

Those are SunSpec 'Not Implemented' sentinel values, meaning the battery does not expose that data point for its chemistry or configuration. Unsupported optional registers in Model 802 must be set to the appropriate unimplemented value per the SunSpec specification. Check whether your battery model documents which points are mandatory versus optional.

Voltage and current readings look wrong by a factor of 10 or 100.

Every measurement register in Model 802 has a paired scale-factor register (v_sf, a_sf, w_sf, etc.). The raw register value must be multiplied by 10 raised to the power of the signed scale factor. Confirm that your portal or polling client is applying the correct sf register to each measurement rather than treating the raw value as the final number.

The gateway connects but no data appears after importing the template.

SunSpec devices place Model 802 at a dynamic offset within the holding register space, not at a fixed absolute address. The SunSpec scan must first locate the SunS marker (0x5375 0x6E53) at address 40000, 0, or 50000, then walk the model chain to find Model 802. If the polling client uses a hard-coded start address it will miss the block. Verify the unit ID and confirm the SunSpec scan completes before reading offsets.

Is it safe to write socrsvmin, socrsvmax, setop, or setinvstate remotely?

Use caution with all write registers. Writing setop or setinvstate can trigger immediate connect, disconnect, or charge commands on the battery bank, which may trip protection circuits or violate the battery management system's operating envelope. Confirm acceptable ranges with the battery manufacturer before writing, and coordinate with on-site personnel when issuing commands remotely.

Free Modbus template: SunSpec Model 802 — Battery Base Model

Name: SunSpec Model 802 — Battery Base Model
Brand: SunSpec
SKU: 4576b0da-a15a-4bf8-b02b-affb477586d2

SunSpec Model 802 is the Battery Base Model defined by the SunSpec Alliance, the mandatory foundation register block that all SunSpec-compliant battery storage systems must expose. Using Modbus TCP, this template reads nameplate ratings (amp-hour and watt-hour capacity, maximum charge and discharge power), live measurements (state of charge, depth of discharge, state of health, cycle count, DC voltage, current, and power), cell-level voltage extremes, and event bitfields for fault detection. Write registers allow remote control of reserve SoC limits, operation commands, inverter state, and alarm resets. One template covers any SunSpec 802-compliant battery regardless of chemistry or manufacturer.

Registers (58)

58 read / 6 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 802 for Battery Base Model.	0	FC03	uint16		R
l Length of this model block in 16-bit Modbus registers.	1	FC03	uint16		R
ahrtg Nameplate charge capacity of the battery bank in amp-hours.	2	FC03	uint16	Ah	R
whrtg Nameplate energy capacity of the battery bank in watt-hours.	3	FC03	uint16	Wh	R
wchartemax Maximum continuous charge power rating in watts.	4	FC03	uint16	W	R
wdischartemax Maximum continuous discharge power rating in watts.	5	FC03	uint16	W	R
discharte Self-discharge rate as a percentage of rated energy capacity.	6	FC03	uint16	%WHRtg	R
socmax Maximum permitted state of charge, as a percentage of rated energy.	7	FC03	uint16	%WHRtg	R
socmin Minimum permitted state of charge, as a percentage of rated energy.	8	FC03	uint16	%WHRtg	R
socrsvmax Writable upper reserve state-of-charge limit, percentage of rated energy.	9	FC03	uint16	%WHRtg	R/W
socrsvmin Writable lower reserve state-of-charge limit, percentage of rated energy.	10	FC03	uint16	%WHRtg	R/W
soc Present state of charge, as a percentage of rated energy capacity.	11	FC03	uint16	%WHRtg	R
dod Present depth of discharge as a percentage of nameplate capacity.	12	FC03	uint16	%	R
soh State of health, remaining battery life as a percentage.	13	FC03	uint16	%	R
ncyc Cumulative number of full charge-discharge cycles completed.	14	FC03	uint32		R
chast Charge status enumeration: idle, charging, discharging, or full.	16	FC03	uint16		R
locremctl Control mode flag: local operator or remote control active.	17	FC03	uint16		R
hb Heartbeat counter incremented by the battery management system.	18	FC03	uint16		R
ctrlhb Writable heartbeat counter expected from the external controller.	19	FC03	uint16		R/W
almrst Writable alarm reset register: write 1 to clear latched alarms.	20	FC03	uint16		R/W
typ Battery chemistry type enumeration, e.g. lithium-ion or lead-acid.	21	FC03	uint16		R
state Operational state of the battery bank, e.g. initializing, ready, or fault.	22	FC03	uint16		R
statevnd Vendor-specific battery bank state code, interpret per manufacturer docs.	23	FC03	uint16		R
warrdt Remaining warranty period in days as reported by the battery system.	24	FC03	uint32		R
evt1 Primary event bitfield: standard alarm and fault flags for the bank.	26	FC03	uint32		R
evt2 Secondary event bitfield: additional standard alarm and fault flags.	28	FC03	uint32		R
evtvnd1 Vendor-specific event bitfield 1 for manufacturer-defined fault codes.	30	FC03	uint32		R
evtvnd2 Vendor-specific event bitfield 2 for manufacturer-defined fault codes.	32	FC03	uint32		R
v Instantaneous DC bus voltage of the battery bank in volts.	34	FC03	uint16	V	R
vmax Maximum DC bus voltage recorded for the battery bank in volts.	35	FC03	uint16	V	R
vmin Minimum DC bus voltage recorded for the battery bank in volts.	36	FC03	uint16	V	R
cellvmax Highest individual cell voltage currently measured in the bank, volts.	37	FC03	uint16	V	R
cellvmaxstr String index containing the cell with the highest voltage.	38	FC03	uint16		R
cellvmaxmod Module index within the string containing the highest-voltage cell.	39	FC03	uint16		R
cellvmin Lowest individual cell voltage currently measured in the bank, volts.	40	FC03	uint16	V	R
cellvminstr String index containing the cell with the lowest voltage.	41	FC03	uint16		R
cellvminmod Module index within the string containing the lowest-voltage cell.	42	FC03	uint16		R
cellvavg Average cell voltage across all cells in the bank, volts.	43	FC03	uint16	V	R
a Instantaneous DC current into or out of the battery bank, amperes.	44	FC03	int16	A	R
achamax Maximum instantaneous DC charge current allowed, amperes.	45	FC03	uint16	A	R
adischamax Maximum instantaneous DC discharge current allowed, amperes.	46	FC03	uint16	A	R
w Instantaneous power flowing to or from the battery bank, watts.	47	FC03	int16	W	R
reqinvstate Inverter state requested by the battery management system, enumeration.	48	FC03	uint16		R
reqw AC power requested by the battery from the inverter, watts.	49	FC03	int16	W	R
setop Writable operation command: instructs the bank to connect, disconnect, or charge.	50	FC03	uint16		R/W
setinvstate Writable register to set the requested inverter state from the controller.	51	FC03	uint16		R/W
ahrtg_sf Scale factor applied to the AHRtg charge capacity register.	52	FC03	int16		R
whrtg_sf Scale factor applied to the WHRtg energy capacity register.	53	FC03	int16		R
wchadischamax_sf Scale factor applied to max charge and discharge power registers.	54	FC03	int16		R
discharte_sf Scale factor applied to the self-discharge rate register.	55	FC03	int16		R
soc_sf Scale factor applied to all state-of-charge percentage registers.	56	FC03	int16		R
dod_sf Scale factor applied to the depth-of-discharge register.	57	FC03	int16		R
soh_sf Scale factor applied to the state-of-health register.	58	FC03	int16		R
v_sf Scale factor applied to all DC bus voltage registers.	59	FC03	int16		R
cellv_sf Scale factor applied to all individual cell voltage registers.	60	FC03	int16		R
a_sf Scale factor applied to the DC current register.	61	FC03	int16		R
amax_sf Scale factor applied to max charge and discharge current registers.	62	FC03	int16		R
w_sf Scale factor applied to the instantaneous power register.	63	FC03	int16		R