Inconsistent battery life when using fitness app in Hiking Mode,

Thanks for posting in the Apple Support Communities meesterbeel,

The following guidance will help you optimize power use on your Apple Watch to improve the overall time the device is able to run before the battery depletes.

Update to the latest software.

Always make sure your Apple Watch is using the latest version of watchOS.

* To see if you need an update, open the Apple Watch app on your iPhone and go to My Watch > General > Software Update.

* If an update is available, connect your iPhone to Wi-Fi, attach the charger to your Apple Watch (make sure it has at least 50% charge), and update wirelessly.

Learn more about updating watchOS

Adjust your settings.

There are a few ways you can preserve battery life on your Apple Watch:

* During running and walking workouts, turn on Power Saving Mode to disable the heart rate sensor. To do this, open the Apple Watch app on iPhone, go to My Watch > Workout, and turn on Power Saving Mode. Note that when the heart rate sensor is off, calorie burn calculations may not be as accurate.

* For longer workouts, you can choose to use a Bluetooth chest strap instead of the built-in heart rate sensor. To pair the Bluetooth chest strap with your watch, make sure the strap is in pairing mode, then open Settings on Apple Watch, select Bluetooth, and choose from the list of Health Devices.

* If you’re very active with your hands and your watch display turns on more than you think it should, you can prevent the display from turning on every time you raise your wrist. Open Settings on Apple Watch, select General, select Wake Screen, and turn Wake Screen on Wrist Raise off. When you want to turn on the display, just tap it or press the Digital Crown.

* Disabling Bluetooth on your iPhone increases the battery drain on your Apple Watch. For more power-efficient communication between the devices, keep Bluetooth enabled on iPhone.

Enable Low Power Mode.

Introduced with watchOS 9, Low Power Mode is an easy way to extend the battery life of your Apple Watch when needed, for example if you’re on a long flight or find yourself without your charger for the night. You can enable it by swiping up to Control Center and tapping on the battery percentage, or by going to Settings > Battery. 

Low Power Mode prolongs battery life by turning off always-on display, limiting the cellular and Wi-Fi connections of your Apple Watch, and disabling background sensor readings including heart rate measurements, high and low heart rate notifications, irregular rhythm notifications, and blood oxygen measurements.

When not connected to your iPhone, your Apple Watch will attempt to retrieve notifications approximately once an hour. When your Apple Watch battery reaches 80% charge Low Power Mode automatically switches off.

View Battery Usage information

To view your battery usage and charging history, open the Settings app on your Apple Watch and go to Battery.

Maximizing Battery Life and Lifespan - Tips for Apple Watch

We hope this helps!