Q: iPhone 6 Plus will download

Try to force restart the phone by holding the sleep and home button for about 10sec, until the Apple logo comes back again. You will not lose any data by doing that, but it can cure some glitches.

If this does not help, setting it up as new device would be the next step:

How to erase your iOS device and then set it up as a new device or restore it from backups

Maybe also take a look at this page about battery drainage