Hi excell,
If your device stopped charging at 80 percent
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.
here's the article where it came from: If your iPhone, iPad, or iPod touch won't charge - Apple Support
good luck
Charles