BARCELONA • Samsung has addressed the major criticisms levelled against its current Galaxy S6 series with its upcoming Galaxy S7 and S7 edge smartphones.

The South Korean tech giant has reintroduced expandable storage - notably missing in the Galaxy S6 and S6 edge - and ramped up battery life in the latest models to recapture lost market share.

The new 5.1-inch Galaxy S7 and the 5.5-inch S7 edge were unveiled yesterday, a day before the start of the annual Mobile World Congress in Barcelona, Spain.

Research firm Gartner said Samsung lost market share to Apple in the second quarter of last year, due partly to the lack of expandable storage and the mediocre battery life of Samsung's flagship S6 series.

Although still the top smartphone maker in the world, Samsung's share of the global market slipped to 19.9 per cent in the second quarter of last year, from 26.2 per cent in the same period in 2014.

With the Galaxy S7 series, Samsung has also included a hybrid SIM card-storage tray for holding either two SIM cards, or a SIM card and microSD storage card. The device supports up to 200GB of additional storage.

The battery life of the upcoming new models has also been improved to 3,000 mAh for the S7 and 3,600 mAh for the S7 edge. The S6 battery capacity is only 2,550 mAh, and the S6 edge, 2,600 mAh.

Samsung has also brought back features such as water resistance, last seen on the Galaxy S5 series. The two new phones can be submerged 1m underwater for over 30 minutes.

Both phones will be available from the middle of next month.

Yesterday, Samsung also announced the Gear 360 for taking 360-degree pictures and videos. While 360-degree cameras are not new, the Gear 360 is the first attempt by a major phone maker.

The spherical device comes with two 15-megapixel fish-eye lenses placed back to back for shooting both stills and videos. It has a microSD card slot for up to 128GB of additional storage. The camera does not have a viewfinder, but if synced with selected Samsung smartphones, a real-time feed from the camera can be seen on the phone's screen, and images and videos can be directly uploaded to sites such as YouTube and Facebook.

The Gear 360 will be available from the second quarter of this year in selected countries.