Why does my phone only work when it’s on charge

I have dropped my phone a couple of times and it was still working perfectly until this afternoon where it suddenly started to restart constantly and wouldn’t turn on unless if i put it on charge. when i take it off of charge, it stops working and goes back to restarting. my battery health is at 100% and i recently got a new one. it says that i have 48% but it still keeps on restarting.