Battery losing capacity and adapter not working on 4k

I bought an XPS 13 Plus 9320. It came with Ubuntu. Things had gone great; I liked the product overall. Its size is perfect, the 4K screen is amazing, and the performance is nice. USB-C is fine for me because I already have USB-C peripherals. But I noted something not so well; the battery lost 10.9% of its original capacity in only 3 months. I've already set the UEFI to run the computer cooler and to optimize the battery longevity when I saw it losing 4.5% capacity in the first month and still lost another 6.5% later. I'm afraid it is a defect or the battery is of poor quality.

There is another issue; I can't make my generic HDMI adapter work on 4K or any resolution above 1080p, but when I plug the same adapter into my phone it works on Quad HD just fine. I looked on the web for a solution, but it seems it is a config on Wayland/Xorg. I haven't figured out why it isn't outputting above 1080p yet.