Exclusive: The secret behind the OnePlus Watch 3’s epic 120-hour battery

The OnePlus Watch 2 already had industry-leading battery life, offering 100 hours in its Wear OS mode or a whopping 12 days in a battery-saving mode, but the new OnePlus Watch 3 boosts that to 120 hours and 16 days respectively.

The question is, how has OnePlus managed to do this when Wear OS rivals like the Samsung Galaxy Watch 7 offer a single day of battery life? 

Well, I had the exclusive chance to discuss all things OnePlus Watch 3 with Dr Zijing Zeng, Head of Research & Development and Head of the OnePlus Health Lab, whose team has been leading many of the wearables’ innovations – and the answer is surprisingly simple.

You see, it relies mainly on the OnePlus Watch 3’s combination of a CPU and an MPU (microprocessor unit) and how OnePlus utilises the two sensors for different purposes.

“Below the CPU, we have a very powerful MCU” Zeng explained. “As far as fitness [and] health tracking sensors, those are all on the MCU level” while the CPU focuses solely on running the OS itself. 

The competition, including high-end alternatives like the Galaxy Watch Ultra, runs both the OS and sensors on the CPU. “So this means every time the sensor is collecting data, it’s processing everything on the CPU” which has a knock-on effect on battery life. 

It’s like a hybrid car

Zeng explained that it’s much like the design of a hybrid car, with a large petrol motor for longer trips and a battery for shorter trips, providing better overall efficiency.  

It helps that users don’t always hammer the CPU with OnePlus’s configuration. “Usually when people wear these [watches], they’re not playing games”. Instead, “most of the time it’s the sensors working in the background” with the occasional trigger of the screen to run apps, check notifications or listen to music. 

Importantly, Zeng explained, “those are very short [instances]” that effectively allow the low-powered MCU to bear most of the daily grunt.

Of course, it’s not just the optimised chipset design that aids in this endeavour. The OnePlus Watch 3 also sports an LTPO-enabled display that lets it drop down to 1Hz when not in active use, ideal for the AOD mode, and there’s a bigger battery, up from 500mAh to 631mAh. 

This combination of technologies is what allows for such exceptional battery life. It also helps explain why we’ve not seen smartwatches come close to the OnePlus Watch 2’s 100-hour battery life, let alone the boosted 120 hours from the new OnePlus Watch 3. 

For more on the new wearable, read my full, in-depth OnePlus Watch 3 review before its release on 25 February.