Amazfit Balance 3 Cycling and Swimming Accuracy Tested: Real Numbers

The Amazfit Balance 3 put in a serious shift at the Dartmoor Classic, covering 108 km in 26°C heat with optical PPG heart rate that tracked near chest-strap accuracy for most of the ride. That is a meaningful result. Wrist-based optical sensors use light to measure blood volume changes, and heat plus heavy sweating are exactly the conditions that wreck that signal on cheaper hardware. The Balance 3 mostly held up.

Heart Rate and GPS Accuracy on the Bike

Over the Dartmoor Classic route, HR data from the Balance 3's PPG sensor stayed close to chest-strap electrical readings across sustained climbs and tempo efforts. Where it drifted was predictable: hard, short accelerations out of corners and any moment where wrist contact got inconsistent. GPS tracked well on open moorland but showed drift on tree-lined descents, which is a known satellite signal issue when canopy blocks sky view, not a flaw unique to Amazfit. The Garmin Epix Pro Gen 2 (currently $499 in Prime Day deals) handles multiband GPS better in those conditions, pulling from multiple frequency bands simultaneously. The Balance 3 runs single-band. For 90% of cycling routes, you won't care. For technical forests or urban crits, you might.

The hDrop sweat sensor adds an interesting layer, measuring sweat electrolyte data during the ride. Sodium loss estimates during a 108 km effort in summer heat are genuinely useful for dialing hydration strategy. Take the absolute numbers as directional rather than lab-grade, but the trends are consistent enough to act on. Polar and Garmin don't offer anything like this at any price point. Whoop doesn't touch it either.

Swimming: Lap Counting and HR Underwater

In the pool, the Balance 3's lap counting was flawless in testing alongside the FORM Smart Swim 2 LT goggles. Lap counting from a wrist watch uses accelerometer data to detect turns, and the Balance 3 nailed it. HR underwater is a harder problem. Optical PPG sensors fight water turbulence, motion artifact from the stroke cycle, and the optical interference of water itself. The Balance 3's swimming HR picture is described as more nuanced than raw stats suggest, meaning it gets the broad strokes right (pun intended) but individual interval data can be noisy. The Apple Watch Ultra 3, also discounted this Prime Day, uses a similar optical approach and faces the same physical constraints. No wrist watch solves this perfectly. A dedicated chest strap using electrical impulse detection remains the gold standard for swimming HR, but most pools won't let you pair one mid-session anyway.

For triathletes specifically, the Balance 3 covers all three disciplines in one device. The sweat sensor data gives you something a Garmin Forerunner 965 or Coros Pace 3 simply cannot. Lap counts are reliable. Cycling HR is solid on steady-state efforts. That is a usable package for Olympic and 70.3 distance athletes who want one watch across training blocks. You can see a full breakdown of the Balance 3's sensor suite in our [Amazfit Balance 3 tested deep-dive](/en/articles/amazfit-balance-3-tested-hr-gps-swimming-and-sweat-data-2026-07-10).

What Is Missing

The Balance 3 is not a perfect device. GPS multiband is the clearest hardware gap versus Garmin's upper tier. The Garmin Instinct 3 AMOLED at $299 in current Prime Day pricing runs multiband and matches the Balance 3 on durability. Running power is present on the Balance 3 but leans more on algorithmic estimation than dedicated footpod data. Recovery metrics are improving in Zepp OS but still lag behind Garmin Body Battery or Polar Nightly Recharge in terms of longitudinal trend reliability. The sweat sensor is genuinely differentiating, but its accuracy ceiling is still being established by real-world testing. And battery life, while decent, does not touch the Coros Vertix 3 or Garmin Fenix 8 Solar for ultra-distance athletes.

If you are shopping Prime Day 2026 and trying to rank these deals, our [Amazon Prime Day 2026 deals ranked piece](/en/articles/amazon-prime-day-2026-garmin-polar-apple-and-amazfit-deals-ranked-2026-07-13) covers Amazfit, Garmin, Polar, and Apple side by side. The Balance 3 represents strong value for triathletes and cyclists who want sweat data and reliable GPS at a price well below Garmin's flagship tier. Against the Garmin Epix Pro Gen 2 at $499, you are trading multiband GPS and a deeper ecosystem for unique biometric data and a lower price tag. That trade is worth it for athletes who actually use nutrition and hydration data. Not the right call for trail runners deep in the mountains where GPS precision is safety-critical.