XPS 9320: Laggy when unplugged, fast battery drain.

I'm using an XPS 9320 and need support with two issues:

1. Recently, every time I unplug the charger, my laptop becomes very laggy, and all operations respond very slowly. It takes about 5–7 minutes for it to return to normal. However, if I plug the charger back in while it's lagging, it immediately returns to normal—no lag, no stuttering. This issue has been occurring for about a month now. Is anyone else experiencing the same problem? And how should I address it? Thank you.

2. My battery drains much faster now compared to about a month ago (and it's definitely not due to age or battery wear). I checked using the MyDell app, and it shows that my battery health is very good, and I also purchased the laptop not long ago. Previously, I could use it for about 4–5 hours before the battery ran out, but now it drains very quickly, around 2 hours? I feel like after a few Dell updates, my laptop has been getting worse. Could that be the case?