---
title: Charging & LED Indicators
description: LED behavior during charging and operation
---

import { Aside } from '@astrojs/starlight/components';

The NanoVNA-F V3 has two indicator LEDs -- one red and one blue -- located on the top edge of the device. Their behavior communicates the current charging and power state without needing to check the on-screen battery voltage.

---

## LED State Reference

| Device State | RED LED | BLUE LED |
|---|---|---|
| Fully charged (USB connected) | OFF | ON (steady) |
| Normal operation (no USB) | OFF | OFF |
| Low battery warning | OFF | ON (steady) |
| Charging (device off) | ON (steady) | FLASH |
| Charging while operating | FLASH | OFF |

---

## Understanding Each State

### Fully Charged

When the battery is fully charged and the USB cable is still connected, the blue LED remains on steadily and the red LED is off. You can safely disconnect the USB cable or continue operating.

### Normal Operation

During normal battery-powered operation (no USB connected), both LEDs are off. Check the on-screen battery voltage display (region 8) for remaining charge.

### Low Battery

When the battery voltage drops to a low level, the blue LED turns on steadily as a warning. The red LED remains off. Charge the device soon to avoid data loss from unexpected shutdown.

<Aside type="caution">
  Charge the device when the on-screen voltage reading drops below 3.3 V. Operating at very low voltage may cause measurement inaccuracy before the device shuts down.
</Aside>

### Charging (Device Off)

When the device is powered off and connected to USB for charging, the red LED is on steadily and the blue LED flashes. This is the normal charging indication.

### Charging While Operating

When you continue using the device while it charges over USB, the red LED flashes and the blue LED is off. The device is simultaneously drawing power for operation and charging the battery.

---

## Charging Guidelines

| Parameter | Value |
|---|---|
| Charging interface | USB Type-C |
| Charging voltage | 4.7 V to 5.5 V |
| Battery capacity | 4500 mAh (3.7 V lithium-ion) |
| Typical battery life | Up to 5 hours |
| Full charge voltage | Approximately 4.2 V |
| Low battery threshold | Below 3.3 V |

<Aside type="tip">
  The NanoVNA-F V3 also provides a USB-A power output port rated at 5 V / 1 A, which can be used to charge other devices. This output is active when the NanoVNA-F V3 is powered on.
</Aside>

---

## Troubleshooting

**LEDs do not light up at all during charging:**
- Verify the USB cable is properly seated in the Type-C port
- Try a different USB cable or power source
- Ensure the power source provides at least 4.7 V

**Device will not power on:**
- If the battery is deeply discharged, connect USB power and wait several minutes before attempting to power on
- The device can operate while charging if the battery is too low to start on its own

**Battery life is shorter than expected:**
- Higher brightness settings consume more power -- reduce to 60% or 40% for field work
- Continuous sweeping with maximum points (801) uses more power than lower point counts
- Cold temperatures reduce effective battery capacity