Hello DavyFromNL!
Thanks for reaching out to the Apple Support Communities. I understand you’ve noticed changes in the battery performance following the upgrade to macOS Catalina. Not to worry, I have some troubleshooting steps that should help.
First, there was a supplemental update to macOS Catalina released after you posted your message. If you have not already done so, install the update and wait 24 hours. See if there is any change in the performance.
If there is not, check out the information in this article: See how apps affect Mac performance, battery runtime, temperature, and fan activity. If there is nothing showing in Activity Monitor, move on to this article which will give you more details about your MacBook battery: About Mac notebook batteries.
Cheers!