I have a Samsung Galaxy Note 4. After a couple of years of use, I decided to buy a new battery because the old one did not hold charge as it should have. With the new battery, however, the phone would suddenly shut off, without warning and without rebooting. I thought it was a problem with the new battery. Maybe it failed to make proper contact. So I bought a second new battery. Exactly the same happens. I cannot replicate the problem, but I have some observations as to the circumstance in which it happens: 1. I believe that the screen must be on for the phone to shut down. It does not turn off by itself on my pocket or when the lid is closed. 2. It has nothing to do with moving the phone. I can have the phone lying flat on a sturdy surface, swicht it on, and then try to do something like opening an app or something without taking the phone off the surface, and the phone might shut down. 3. Once it has shut down, I cannot immediately turn it on. What I used to do until yesterday was to remove the battery and put it back on, and then it would turn on as if nothing had happened. Yesterday I realised another interesting fact: if after shutdown I plug the charger in, there will be a three-step process: first, i'll see on screen the icon for charging an entirely depleted battery (though the battery might be 70% or so), so I unplug/plug the charger, I get to the second step: the phone will display the “not charging” icon (i.e. a battery with a yellow triangle on it); unplug/plug to get to the third step: I will see the icon showing that the battery is (say) 70% and then i will be able to switch the phone on. 4. I believe that when it is connected to the charger the phone will not shut down, but I am not so sure of this (I have been observing how the fact that is plugged affects the phone’s behavior since yesterday only) Any help will be greatly appreciated.