When Apple Senior Vice President of Operations Jeff Williams unveiled the cellular-capable Apple Watch Series 3 in Cupertino yesterday, he touted a fairly impressive 18-hour battery life. Indeed, Apple’s product page says “up to 18 hours,” and that “all day” figure matches the non-cellular Series 3 model, as well as last year’s Series 1 model, which has a slower CPU.

But dig into the footnotes on that battery life figure, and you’ll see 18 hours only applies to “casual use.” For specific tasks on the watch, time estimates can drop precipitously:

• Up to 10 hours of local audio playback
• Up to 10 hours of workout with heart rate
• Up to 5 hours of workout with heart rate and GPS
• Up to 4 hours of workout with heart rate, GPS and LTE
• Up to 3 hours for a Bluetooth-connected phone call
• “Over 1 hour” for an LTE-connected phone call

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That means the Watch’s marquee feature — the ability to make phone calls without being tethered to an iPhone — is the activity that will use up the battery fastest of all. That’s extremely disappointing, if not entirely surprising: Last year’s Series 2 watch took a big hit when GPS was turned on, for instance.

The Apple Watch goes on sale alongside the iPhone 8, 8 Plus and Apple TV on Friday, September 22, and the cellular version will add an extra $10 a month to your bill on most US carriers. But you might want to wait for our eventual hands-on review — where battery testing and talk time will be a primary focus — before preordering it this Friday. 

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Apple Watch Series 3: Once more, with calling

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