Apple has started a program for a problem affecting some iPhone 6s that has not been widely reported on.
Some devices that were manufactured between September and October 2015 are experiencing unexpected shutdowns between 20% – 40% mark.
Replacement Process Choose one of the service options below to have your battery replaced. Your iPhone will be examined prior to any service to verify that it is eligible for this program and in working order.
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Please call your service provider to confirm that battery replacement service is available on the day you visit them.
• Apple Authorized Service Provider
• Apple Retail Store – Make an appointment.
• Apple Technical Support – Contact Apple support.
Apple does Note that Wireless carrier partners are not participating in this program. And advisers users to prepare your iPhone 6s for the battery replacement process, please follow the steps below: • Back up your data to iTunes or iCloud. • Turn off Find my iPhone • Erase data and settings in Settings > General > Reset > Erase all Content and Settings.
So if you are jailbroken you must be prepared to lose your jailbreak. You can read the full notice from Apple here.