Please help! Battery stops charging at lower and lower percentages (UX330U Zenbook)

Hi - this problem began a month ago. My laptop would be fully plugged in and charging/resting, but the battery would say it's only at 84%. Every day, the max percentage would go down. Now, it's perpetually plugged in and perpetually at 12%, and I'm beginning to really feel the lag/slowness in loading, scrolling, sending messages, etc.

I've troubleshooted tech problems on my own in the past, generally by relying on Google, but this is the first time that I literally could not find any other info whatsoever about my predicament. I'm a student taking classes online and I need my laptop pretty much all of my waking hours, so you can imagine how worried I am for when that percentage inevitably gets to 0%.

I've had this laptop for almost three years, and one thing of note that I can think of is that a year ago, I spilled ramen soup on some of the keys (and some might have gotten into that vent-looking area between where the laptop folds). But at the time I immediately turned my laptop off and did my best to clean/dry everything, and it's been alright since.

Do you think soup is the culprit? Are my laptop batteries dying somehow? I'm worried this isn't a glitch or bug I can easily fix, and I might actually have to get it sent in to be fixed - this would be terrible news as in these quarantined times I literally can't survive a day without my laptop (I need it for both school and work, every day).

Any help would be greatly greatly appreciated!

Edit: I just downloaded something called BatteryInfoView. As you can see, the current full capacity is "listed" as being 31.7% of the original (already very low), but the current capacity value only charges up till 11.6% maximum (this is after leaving my laptop sitting there for an hour with no major applications running). Why is the capacity falling so fast??