Why does phone only stay on when plugged in to charger?

[Android Central Question]

Hi, my husband has a Galaxy Note 3. It has been giving problems. And the battery was not holding a charge, etc. So we bought a new battery. It worked perfectly for about 6 days and now it only stays on when it's on charge. As soon as you unplug the phone it switches off. The battery says 100%. He even reset the phone yesterday, but still the same problem.
What could it be?
Is the phone just too old? But why does it work perfectly when on charge?

 

[B. Diddy]

Welcome to Android Central! There could be a problem with the battery contacts, or some other internal power circuitry. The only thing you can do is to check the battery contacts and make sure they're clean (and that the battery fits snugly when you snap it in). Otherwise, take it to a repair shop, or look into buying a new phone.