Buy a PS4 battery and replace it. Very very easy.
[guide|22074]
Guide to fix it. 5 short simple steps.
https://www.ebay.com/itm/Rechargeable-Battery-for-PS4-Controller-2000mAh-Replacement/113281313791?hash=item1a6017abff:g:tVkAAOSwen9aI-Rv
That link is to buy an replacement. Overall cheap but I think it should be cheaper. About 10$
They are all over the internet though, feel free to search another up.
Do those steps and it should fix your controller bud! Just sounds like an battery issue.