Should I attempt to replace the battery on my phone

My phone has an odd issue where it force shuts down (black screen, no shutdown screen) when the battery drops below about 70% and the phones resources are being used. ie: cpu or ram, not sure. Once this happens it when i try to turn it on it will boot to lock screen but when signing in crashes again (probably because starting processes i imagine) unless it is charging. I have tried using a different OS (custom rom) with no success and I am now wondering if i should invest in trying to replace the battery?