iPhone IMMEDIATELY dies unless Charging

Hi.

I'm new to this site, so hopefully I've posted in the right section aha.

TL;DR - My iPhone will literally die unless there's charge going to the iPhone. Once the charger's disconnected from the iPhone, the phone will die.

Once I'm charging the iPhone, it will begin to show the boot logo but in a loop over and over (till about 5-10 minutes have passed) then I can access the phone.

The charging icon at the top-right will ALWAYS show '1%' and shows it's charging. Rarely, I've seen it go up to '2%' but that's as far as it goes. Leaving it on overnight to charge or leaving it to charge for an hour won't do anything.

I want to fix it but I don't know what's actually the problem. People are giving me different opinions such as the "battery may be on it's last legs" or "the connector to the charging port may have come undone..".

Any help will be appreciated. Thank you! :)