Apple has promised to replace faulty batteries in some of its iPhone 6s smartphones that cause the device to shut down unexpectedly.

The company confirmed rumours surfacing over the past week that some of its iPhone 6s devices were switching off without warning.
However, Apple denied the problems represented a "safety issue" as seen with the exploding batteries in rival Samsung's Galaxy Note 7 devices.
It said affected phones were made between September and October last year and came from a "limited" range of serial numbers. Apple did not detail how many devices were impacted by the battery issue.
Reports from affected customers indicate the unexpected shutdown occurs once the battery charge is sitting between 50 and 60 percent.
Apple has advised customers to visit one of its stores or an authorised service provider to check their phone's serial number and determine whether the device requires a new battery.
While it has offered replacement batteries for affected devices free of charge, Apple said any existing damage to the phone that affects the replacement of the battery will need to be resolved before the repair.
The company last week was forced to acknowledge that some iPhone 6 Plus devices suffer from what users have nicknamed the "touch disease", which causes the phone screen to become unresponsive.
Apple is now offering affected users a discounted, fixed-cost repair for A$228.95. It also said it would cover any costs above that amount for customers who have already paid to have their devices fixed.
The company is facing a class action law suit in California over the "touch disease" issue. Apple denied the problem was due to the design of its device, arguing instead the touchscreen becomes unresponsive after the phone has been dropped multiple times on a hard surface.