Chosen Solution

Just replaced the batter in my 6sPlus and powered it on to make sure if worked before putting everything back in place and now it won’t shut down.

Maybe connect it to a PC and try an update through iTunes, otherwise it could be a dud battery

Even try hard resetting it:

  1. holding home + power button until the phone shuts off and you see an apple logo.
  2. If iTunes won’t work either, you will need to get a new battery and replace it again.