iPhone shuts of every 2 mins so can't complete update fully

Are you saying your old device has an issue where it won’t stay on and is the reason you have a new phone? If so you likely will need to back it up while it is connected to a power source or use a computer to do it. If those options won’t work you will either need to setup the new phone with an old back up or set it up as a new device retrieving whatever data you have in iCloud if any.

Need some basic information:

• What is the model of the old phone?
• What is the model of the new phone?
• What iOS version is on the old phone?
• What iOS version is on the new phone?
• Is it the old phone or the new phone that shuts off every 2 minutes?
• What is the battery health of each phone?
• Are both phones plugged in to power when trying to update?