Battery Offset

The NanoVNA-H displays battery voltage to help monitor charge level. The voltage reading can be calibrated to match your multimeter for accurate monitoring.

Why Calibrate Battery Voltage

The battery voltage reading may be inaccurate due to:

Component tolerances in the voltage divider
ADC reference variations
Different battery types

Calibration ensures the displayed voltage matches reality.

Check Current Reading

Via Display

The battery voltage appears in the status area when:

No USB power is connected
Battery is installed
Device is running on battery

Via Shell Command

vbat

Returns the battery voltage in millivolts.

Measure Actual Voltage

Disconnect USB power
Use a multimeter to measure actual battery voltage
Note the displayed voltage on the NanoVNA-H
Calculate the difference

Calculate Offset

The offset is the difference between actual and displayed voltage:

Offset = Actual_mV - Displayed_mV

For example:

Multimeter shows: 3850 mV
NanoVNA displays: 3800 mV
Offset needed: +50

Or if the display reads high:

Multimeter shows: 3750 mV
NanoVNA displays: 3800 mV
Offset needed: -50

Set Battery Offset

Via Shell Command

# Set offset (in millivolts)
vbat_offset 50     # Add 50 mV to reading
vbat_offset -30    # Subtract 30 mV from reading

# Query current offset
vbat_offset

Save the Setting

After calibration:

saveconfig

Verification

After setting the offset:

Run vbat command
Compare with multimeter reading
Adjust offset if needed
Save configuration

Battery Voltage Ranges

Typical lithium-ion battery voltages:

State	Voltage
Full charge	4.2V
Nominal	3.7V
Low	3.4V
Critical	3.2V
Empty	3.0V

USB vs Battery

When USB is connected:

Device is powered by USB
Battery may be charging
Voltage reading may show charging voltage (up to 4.2V)

For accurate battery-only readings, disconnect USB.

Practical Example

Disconnect USB, run on battery
Measure battery with multimeter: 3.82V (3820 mV)
Run vbat command, shows: 3780 mV
Calculate offset: 3820 - 3780 = +40
Set offset: vbat_offset 40
Verify: vbat now shows 3820 mV
Save: saveconfig

Troubleshooting

Voltage Always Shows 0

Battery may not be connected properly
ADC may not be reading (hardware issue)

Voltage Fluctuates

Normal under load (sweep uses more current)
Check battery connections
Battery may be worn out

Display Shows Wrong Voltage Even After Calibration

Re-verify multimeter reading
Try a fresh battery for comparison
Check that offset was saved

Shell Command Summary

# Read battery voltage
vbat

# Set voltage offset (millivolts)
vbat_offset 50

# Query current offset
vbat_offset

# Save configuration
saveconfig