Battery Voltage Callouts / Low Voltage Voice Alerts on Any EdgeTX Radio – Setup Guide

This is a simple but extremely useful trick: press a button and your radio tells you the quad’s battery voltage. You can easily set this up on any EdgeTX radio, and it is especially useful for pilots who do not have OSD. I will also show an advanced setup where your radio automatically alerts you when the drone’s battery voltage gets low. This is ideal if you become too focused on flying to constantly check your voltage.

Prerequisites

• Your radio is running EdgeTX
• Your quad supports telemetry (radio links such as ExpressLRS and Crossfire work)

Further Reading:

Why Use Battery Voltage Voice Callouts?

You want to avoid over-discharging your LiPo battery, so being able to check battery voltage at any time is essential.

If you are too busy monitoring the OSD during flight—or if your quad does not have OSD at all (for example, when flying line of sight without goggles or a screen)—audible voltage callouts are extremely helpful.

Further reading: Understand the importance of monitoring battery voltage and different ways to check it: https://oscarliang.com/monitor-measure-battery-voltage-alarm-drone/

Voltage Callout Using a Switch

With the press of a switch—ideally a momentary switch, though any switch will work—your radio tells you the drone’s voltage.

Step 1: Make Sure Telemetry Is Working

Before setting anything up, confirm that telemetry is working on your quad. When telemetry is working, the quad will be constantly sending data to your radio, including battery voltage.

In Betaflight Configurator

1. Go to Receiver tab
2. Ensure Telemetry is enabled
3. Save and reboot

On the Radio

1. Power on your quad (props off)
2. On your radio:
   1. Open Model Settings (press the MDL button once)
   2. Navigate to the Telemetry page (press PAGE)
3. Scroll down to Sensors and select “Discover new”
4. Within a few seconds, a list of telemetry sensors should populate.

What you are looking for is:

• RxBt (receiver battery voltage)

When a battery is plugged into the drone, this value should update in real time (how often it updates depends on your telemetry ratio setting in ExpressLRS LUA script).

Step 2: Verify Battery Voltage Accuracy

Confirm that the RxBt voltage reading is accurate using a multimeter or a battery voltage checker (get your voltage checker here)

If the value is incorrect, you may need to calibrate it in Betaflight under the Power & Battery tab. This is rare—most flight controllers work correctly out of the box.

Step 3: Assign a Momentary Switch to Speak Voltage

Go to Special Functions

1. Open Model Settings (press MDL button once)
2. Navigate to Special Functions (press PAGE button to get there)
3. Select an empty line and click Enter button

Configure the Function

Set the following:

• Switch: Choose a unused switch (preferably a momentary button, e.g. SH↓ in the GX12)
• Function: Play Value
• Parameter: RxBt (You may also see RxBt+ and RxBt-, these are the maximum and minimum value recorded during flight. If you just want to check the current battery voltage, use RxBt.)
• !-: this option ensures the value is played only once while the switch is active
• Enable: ✔ Checked

That’s it.

Test it

• Press the assigned switch
• Your radio should say something like: “twenty two point nine volts”.

You now have on-demand battery voltage callout.

Bonus: Reporting Average Cell Voltage

By default, RxBt reports the total LiPo voltage. You can optionally configure it to report average cell voltage, which many pilots find more intuitive—especially when flying quads with different cell counts, you don’t need to do the calculations in your head.

In the Betaflight CLI, enter:

set report_cell_voltage = on
save

Advanced Setup: Low Voltage Warning

If you want to be extra safe—especially if you get immersed in flying and forget to check voltage—you can set up an automatic low-voltage warning.

In this example, the radio will warn you when voltage drops below 3.5V per cell. You can adjust this threshold as needed.

Step 1: Setup Logical Switch

1. Navigate to Logical Switches on your radio
2. Scroll to an empty line (for example, L01) and press ENTER
3. Configure the logical switch as follows:
   1. Function: a
   2. V1: RxBt
   3. V2: 3.5V (you can change it to any voltage you want)
   4. Delay: 3 seconds (this delay reduces false positives caused by voltage sag during punchouts)

Important: Make sure the following CLI command is enabled so RxBt reports voltage per cell set report_cell_voltage = on

Step 2: Create a Special Function

1. Go to Special Functions
2. Add a new line
3. Select the logical switch created in the last step (in our example it’s L01)

Set Function to Play Track or Play Value:

• Choose “Play Value”, and select RxBt to call out the actual voltage.
• Set Repeat Delay: If you want the alert to repeat, set a repeat delay (e.g., 10 seconds). If you only want it to alert once, set it to !.
• ✔ Enable it.

Your radio will now automatically alert you when the battery voltage falls below your set threshold. And it will repeat the warning every 10 seconds as long as the voltage is below that limit.

Or, you can choose “Play Track” instead, and select “lowbat” to play the “low battery” warning. You can even record something unique into an audio file and play it.

Conclusion

Setting up audible battery voltage callouts and low-voltage warnings on your EdgeTX radio significantly improves both safety and situational awareness. It allows you to focus on flying instead of constantly monitoring battery levels.

Whether you prefer manual voltage checks using a switch or automatic alerts based on voltage thresholds, these setups ensure you never miss a low-battery warning again.