An ultra-low-energy 'Power Reserve' mode could help Apple Watch time keep ticking.

Apple has repeatedly said the Apple Watch will last about a day, which means you're going to want to charge it every night so you don't have to take it off when it actually runs out — be it the middle of the night when you're sleeping or early the next day when you'd rather be using it. If something happens and you can't get to a charger in time, however, there might be a time-only "Power Reserve" mode to give you an extra buffer. That's according to Brian X Chen at the New York Times

Apple has said the watch battery is estimated to last a full day, requiring a user to charge it at night, similar to a smartphone. The company also developed a yet-to-be-announced feature called Power Reserve, a mode that will run the watch on low energy but display only the time, according to one employee.

Chen claims the Apple Watch project was codenamed Gizmo, and that Apple also experimented with solar charging before settling on the inductive charging it showed off last September at the watch's introduction.

Battery life remains what you use to pay for every other feature. Want a full color Retina display? Want Bluetooth and Wi-Fi? All of it has to be paid for in battery life, and every feature that lights up the screen or radios is part of the cost. The trick is balancing battery life so that we get the features we want and can use them for an acceptable amount of time.

Apple is holding a Spring Forward event on March 9 where more information on the Apple Watch will be made available.