Samsung Galaxy Note 4: power on off loop:
I have a Note 4 also.. When I updated to one of the newer OS it started power on off looping when the battery got to a low percentage. This would freak out any User. It is normal for many people however. It is a Google software firmware issue that will probably be fixed after the next patch update.
In the mean time, if when your battery gets really low and you get the power on off loop, just charge the device or pop in a charged battery.
There is no fix for this right now. You just have to deal with it.
If your battery is higher then 15% left and it is looping, then the possibility is that either you tried to/or the system automatically tried to update your phone, but the transfer was interrupted or corrupted some how.. could be bad connection between the towers or the WiFi router you were on.. or any number of other things.
If you are in the US, best to drop by a local Best Buy store. Call ahead and ask if they have a Samsung Experience Shop inside. Not all Best Buys have one.
Ask to have Best Buy transfer your call to the rep there if possible (I'm not sure if they have a phone there.. if not you may have to just visit the Best Buy store with the Samsung Experience Shop inside there..
Bring your device and your charging cables/adapter just in case, make sure the battery is charged).. Ask if the Samsung Manager can help you and when s/he will be available.
That person will have the knowledge and the equipment inside the Samsung Experience section to get your phone back to normal again, however note that you may lose all your data files on the phone. It most likely will have to be factory reset and possibly reFlashed with the OEM firmware. WELCOME TOTHE SAMSUNGEXPERIENCE SHOP