Notebook Hardware and Upgrade Questions

Hello all!

I have bought a HP Spectre x360 14 inch 2-in-1 laptop with 32GB RAM and 2TB of space. All the reviewers say it has a battery life of around 13 hours, and others say around 11 hours, so this was my expectation. Now after using it for a few days, the battery drains faster than expected. Also, the battery remainder time goes up and down by a lot. Sometimes at 93% it says that I only have 3 hours to go, and then a bit later it says 10 or even 18 hours. But in general, I think I can get around 6/8 hours, which is ok but less than expected and with battery saver on, screen on 30% and fans on battery saver.

Did a quick check and it drains around 1% per 5 minutes, which comes down to around 8 hours. Now using: Whatsapp, Microsoft Edge with 5 pages, Outlook, Teams, 1 word document, 2 folders. This is quite normal, on working days 1 PowerPoint open and 2/3 Excels. And even when I watch Youtube videos, It says at 50% that I can do 2 hours screen time, which sounds crazy. 

How is this possible? And can I do something about it? The rest works really great, only the battery disappoints a bit.