Hello Mak_XPS15,

I would suggest few steps would which would help us in isolating the issue further:

1. Check the Battery Health in the BIOS. To enter BIOS Setup, restart the computer and keep tapping F2 key at the Dell logo screen. Check the battery health and make a note of the message. If anything other than your battery is "performing normally", the battery should be replaced.
2. Dell offers a free Battery Diagnostic test, to run the test refer to the Dell Battery Diagnostics site.
3. Also try the suggestions mentioned in article on How to improve your laptop battery’s performance.

For more details, see Laptop Battery FAQs.

Hope this helps!