It may have been slightly overshadowed by three new iPhones – including the mega-expensive, full-screen iPhone X – but Apple's other big announcement, the Apple Watch Series 3, looks on the surface to be a significant upgrade for the record-breaking wearable.

With a similar look and feel to its predecessors, the new Apple Watch's most notable addition is LTE connectivity, which lets wearers make calls without first having to tether to an iPhone using Bluetooth.

In theory, this means you could leave your phone at home and still be able to ring your friends and family. However, new details revealed by Apple concerning the LTE Watch's battery life suggests you might still need your iPhone after all.

As with previous Watch models, Apple's goal for battery life with Series 3 is 18 hours, which it claims both the GPS and GPS+LTE editions are capable of hitting while performing activities "like checking the time, receiving notifications, using apps, and doing a 30-minute workout".

The immediate concern was how drastically an LTE connection (known as 4G in the UK) would impact talk time estimates – and the answer is 'a lot'. While the Apple Watch Series 3 can muster "up to 3 hours of talk time" when connected to an iPhone, an LTE connection drops talk time to "over 1 hour", according to Apple's testing process.

In addition, using the LTE Watch's fitness features with both network data and GPS turned on will drop the battery life to 4 hours for outdoor workouts (5 hours of GPS only). Indoor workouts still come in at roughly 10 hours.

While the talk time figures are a little disappointing, there is good news for audio fans. According to Apple's tests, music playback from Apple Watch to Bluetooth headphones could hit up to 10 hours of battery life.