When Apple announced its Apple Watch wearable last September, there was scarce mention of the device’s battery life, leading to the natural conclusion that battery was posing a problem for the Apple Watch team. At MobiHealthNews, we speculated that a shorter battery life was holding the team back from introducing sleep tracking, increasingly considered a must-have feature on fitness wearables.

Now, thanks to 9t05Mac, we have the first unofficial reports of the Apple Watch’s battery life, and it isn’t much better than predicted: They report the battery will last for 2.5 to 3.5 hours of continuous app use (2.5 for heavy app use and 3.5 for standard app use). Kept purely in passive mode, the watch will last for 3 days, or 4 days in sleep mode. The most likely use pattern is a combination of active/passive use, which would yield a battery life of 19 hours.

Notably, if all the user is running is the Fitness app, the battery will last for 4 hours of active use. That should be fine for most people provided they don’t check their fitness goal progress too obsessively — or aren’t running too many apps in addition to the Fitness app. On the other hand, the main appeal of the Apple Watch over a dedicated fitness tracker is the presence of those other apps.

Apple Watch’s unique approach to fitness tracking seems to require a passive tracker that lasts all day. In September, Apple announced that its Fitness app would present a visual display for goal-tracking made up of three interlocking rings. One ring, called Move would measure calories based on a personal goal set by the user. Another, called the Exercise ring, would measure active minutes, defined as time spent on anything over a brisk walk. Finally, the Stand ring would simply track whether or not the user stands for at least a minute each hour of the day. This last use case suggests that the Fitness app needs to be always-on, not just activated before a run or bike ride.

The Workout app, on the other hand, could be geared at more episodic use, based on what Apple said in its September announcement.

The report states that Apple’s battery woes stem from the companies decision to use a powerful processor and a high quality screen in the device, both of which require a lot of power. Furthermore, 9to5 Mac reports that the battery has been a continuous source of consternation for the Apple Watch team and has contributed to the delay in releasing the device, now set for the end of March.