Hello, EanneVillas! Thank you for posting to the Apple Support Communities.
We understand your situation and how you are noticing that your iPhone will not charge past 80%. We’re happy to research this issue with you to find out what could be causing this to happen.
To start, we’d like to provide you with the following Apple Support article:
If your iPhone or iPod touch won't charge - Apple Support
According to the article above: “Your iPhone might get slightly warmer while it charges. To extend the lifespan of your battery, if the battery gets too warm, software might limit charging above 80 percent. Your iPhone will charge again when the temperature drops. Try moving your iPhone and charger to a cooler location.”.
For help with keeping your iPhone within acceptable temperatures, please use the tips in the following article:
Keeping iPhone, iPad, and iPod touch within acceptable operating temperatures - Apple Support
We hope this information helps you fully charge your device. Please let us know if we can help with anything else.
Cheers!