For its upcoming Watch, Apple is shooting for somewhere between 2.5 and 4 hours of active use and 19 hours of passive use, according to a new report from 9to5Mac. The site says sources with knowledge of the project have offered up new details regarding the wearable’s battery life.

Battery life was one of the many things left out of the initial Apple Watch unveiling last September, but Tim Cook has since said that the device will need to be “charged every night.” The vague explanation has left many users wondering how long the Watch will last in the real world.

9to5Mac’s Mark Gurman says that Apple is aiming for 2 and half hours of “heavy” gameplay or app use, 3.5 hours of standard app use, and 4 hours of fitness tracking. Other interesting battery life goals mentioned include 3 hours of always-on watch mode, and up to 4 days of standby.

The reason for these seemingly low numbers lies within the hardware. Gurman says the S1 chip inside the Apple Watch offers A5-like performance, and its high quality display can refresh at 60 frames per second. These things combined with the various sensors severely drain the battery.

Announced last year, the Apple Watch is expected to launch in March with a starting price of $349. It will be compatible with the iPhone 5 and all newer iOS devices, communicating with them via a built-in Companion application, revealed in the latest developer release of iOS 8.2.

Source: 9to5Mac