After updating iPhone 6 to IOS 9 it will not turn back on.. HELP!

My partner updated his iPhone 6 to IOS 9 and once the battery died, the phone will not charge, therefore wont turn back on.

The charger is not the problem as it works perfectly fine on the iPad.

Has anyone had this problem or can help at all?? There is important stuff on the phone we do not want lost.