shuts off after few minutes and wont remain on without charger

Hi

My phone shuts off after using it for a few minutes won't turn back on without the charger. It can only be used constantly when charged. If it is used without the charger it will turn off after a short while but the battery will appear to be more than 50% charged.

Update: does not turn on at all, not even with a charger.

Replaced battery with a relatively new one from another phone (3 weeks) still doesn't turn on.

It had been reporting to be running out of storage for a while before it wouldn't turn on anymore would that have anything to do with it?

I would be most grateful for help.I'm desperate and I can't find any forum with this exact problem.