Apple knows about apple watch usage in future, So most of the case you might be suffering from low battery any time. At this moment you need to put your Apple watch in almost dead condition means Smartwatch will become simple watch that will only use for the current time. Power reserve functionality works as power saving mode. Here I gave a guide with step by step instructions on how to put apple watch in power saving mode. After that how we can put apple watch normal mode for use smartwatch app after enough battery. Alternatively, you can use the small pocket size external charger for Apple watch.
Note: Apple watch Battery conditions with saving tips are, you can use two days continuously after charge 100% (Full battery).
Steps to Enable/ Disable or put apple watch in power saving mode:
Apple Watch uses on Low battery charging quite interesting but notices that you can only use for time showing purpose, as of discussed in apple watch keynote you can run Power reserve mode for next 72 hours.
Step 1: grip your apple watch on your wrist,
Step 2: Press and hold side button placed below the digital crown.
Step 3: You will see three options: Power off, Power Saver and Lock device.
Now put your device normal battery power mode
In the process of revert back in normal mode, you need to restart or shut down watch. For restart follow the above three step and Tap and hold side button and release when apple logo will be shown.
Note: are you fail in any case first check your device updated with latest iOS 8.3 or newer, then pair Apple watch with iPhone.
Still are you facing some problem Put apple watch in power saving mode and might be confusing due to settings accuracy share with us on the comment.