When I was at home using a Type-C charger for my iPhone XR, it was charging perfectly fine. I got in my car to drive to class (50 minutes), and my battery was at 58%. When I got to class, my phone was still at 58%, even though it had been charging the whole time. Now, I have a charger plugged into my laptop, and the battery fluctuates between 41-43% but never goes past 43. Can anyone help?
The iPhone XR uses a lightning cable for charging, not USB-C. If your devices are not charging, try replacing the charger.
Yeah, I mean the lightning to Type-C, but right now I’m using a USB to lightning. The first charger was working fine, and I bought the second cord last week, which worked earlier today 
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Return it and get a genuine Apple cable and charger. Also, try cleaning your lightning port with electrical contact cleaner.
The charger is an Apple one 
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Ok then, perhaps the new cable is now bad, or the lightning port is dirty or damaged.
I would think it’s the port itself. I’ve noticed I have to wiggle the charger sometimes before it will charge, so I’ll use some compressed air to clean it when I get home.
That may work, or the port might be damaged. It’s an old phone, and the port can be replaced.
Settings > Battery > Battery Health.
What do I do from there?
You’ll be able to see your battery’s capacity and if the phone has noticed any unusual patterns.
The capacity is at 81%, and it doesn’t say anything is wrong with it.
80% is the threshold manufacturers like Apple recommend for battery replacement. Below 80%, it drains really fast; you’re right above that threshold and should probably look into getting the battery replaced once it drops below 80%.