Frontier X3 vs X2: Better battery life, but not better at everything

The Frontier X3 and X2 are much more than standard heart rate chest straps. Their big selling point is ECG-based heart monitoring during exercise, along with metrics such as cardiac strain, breathing rate, HRV and training load.

I’ve reviewed the Frontier X3 and Frontier X2, and spent plenty of time running and training with both. The X3 is easier to live with, especially when it comes to battery life, but the X2 still has a couple of advantages that could matter depending on what you want from it.

Battery life is on another level with the X3

Fourth Frontier rates the X3 for up to four months with around an hour of use per day. The X2 is rated for roughly two weeks. Continuous recording also jumps from 24 hours on the X2 to as much as 14 days on the X3.

The difference was pretty obvious in my own testing as well. With the X2, I found that topping it up every four or five days for around 20 to 30 minutes kept it at 100%. With the X3, I used it heavily for a couple of weeks, including a full night of sleep tracking, and still had more than 90% left.

So while I was already happy with the X2 battery, the X3 changes the relationship you have with the device. I simply don’t think about charging it very often anymore.

There is also the switch from Micro-USB to USB-C. That is nowhere near as important as the battery improvement, but it is one less old cable to keep around.

The X2 is much better if you want the actual ECG

On the X2, I could open a workout afterwards and move through the ECG in 20-second sections. Event markers also appeared on the trace, so it was easy to jump back to a particular moment and see what was happening.

Frontier X3

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View Frontier X3

There is also a live ECG view and a dedicated continuous ECG recording mode. That gave the X2 a layer of detail that most sports chest straps simply do not offer.

The X3 still uses ECG internally for heart rate, HRV and Rhythm Score. What you lose is direct access to the waveform itself, along with the ability to inspect and export it.

That is probably the biggest reason someone might still choose the older model. I did not spend huge amounts of time studying the raw ECG trace, but if that is one of the main reasons you are interested in Fourth Frontier, the X2 gives you more.

The screen has disappeared

Fourth Frontier has kept the same 73 x 24 x 13 mm dimensions, although the X3 weighs 23 grams rather than 25 grams. Visually, though, the main change is that the little X2 display no longer operates on the X3. You just get status LEDs.

Frontier X3

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View Frontier X3

I actually called for this when I reviewed the X2. The screen showed things such as battery life, mode status and a post-workout summary, but its position across your chest made it difficult to use while exercising. Most of the time it was hidden underneath clothing anyway.

So I don’t consider losing it a downgrade. If anything, my only complaint is that Fourth Frontier didn’t take the opportunity to make the X3 smaller once the display was no longer needed.

There are not many other differences once you get past battery life, ECG access, charging and the display. The main one is Bluetooth, with the X3 moving to Bluetooth 6.0 from Bluetooth 5.2 on the X2. In practice, though, that does not change much. Both can stay connected to the Frontier app while broadcasting heart rate to two additional devices. And neither has built-in GPS (only smartphone GPS or from a connected watch) or ANT+.