Source: Withings
Best answer: Various fitness trackers provide excellent battery life, including the wearable devices shown here. You can choose from trackers with replaceable batteries that last for up to 18 months like the Withings Move or rechargeable batteries, such as the one in the Withings Steel HR Sport, that can last up to 25 days.
Months, not days or hours before needing a new battery
Battery life on both fitness trackers and smartwatches gets better with each passing year. Case in point is the Withings Move, which promises 18 months of operation before the included CR2430 button cell needs to be replaced. The advanced activity tracker has been designed for simplicity. In doing so, it looks like a traditional analog watch. Inside, it keeps tracks of walks, runs, sleep, swimming, and more. With the HealthKit-compatible Health Mate app, you can view your trends and improvements over time.
The Withings Move is offered in five colors. You'll also be able to custom design your wearable device by selecting from different dials, cases, activity hands, and wrist bands.
Activity use can affect your fitness tracker's battery life
Certain activities can affect the battery life of your fitness tracker. If you want to extend battery life to its fullest, you can turn off GPS tracking (if your tracker offers it). Other activities that can affect battery life are using sensors, such as heart rate sensors, often. Using a backlight often will certainly cut down on battery life, so to extend battery life, turn off the backlight. You can also experiment with your Bluetooth or WiFi settings to see what works best.
Other wearable devices to consider
The Garmin Vivofit 4 and Moov 3D also include replaceable batteries with long battery life. The Garmin includes a CR2 coin cell battery that lasts up to one year, while the Moov 3D offers a CR123A battery that runs for up to six months.
If you're looking for a fitness tracker with a rechargeable battery, consider the Fitbit Charge 4 (one week between charges), the Withings Steel HR Sport (25 days), or the Wyze Band Activity Tracker (10 days).
Great battery life

Fitbit Charge 4 Fitness and Activity Tracker
When you want a Fitbit
Fitbit's "best (and smartest)" fitness band to date is also the one that offers the most battery life between charges. Available in multiple styles, the Charge 4 is ideally suited for anyone who doesn't want a smartwatch.
Inexpensive and great battery life

Wyze Band Activity Tracker with Alexa Built-in
Affordable and Alexa built-in
With activity tracking, 24/7 heart rate tracking, sleep monitoring, and 10 days between charges, the Wyze fitness tracker is a bargain. It also includes Alexa built-in, so you can get news and notifications on your wrist.
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