This is normal behavior, and does not mean your PopPower is broken! We promise. This is specific to iPhones, and is related to a recent software update. The latest version of iOS (13.1) has a new Optimized Battery Charging setting, and it’s turned on by default. The iPhone stops charging at 80%, and then tries to predict when you’ll use your phone next while it prepares to charge the remaining 20%. Apple has implemented this change to support your phone battery’s overall health! You can turn this setting off if you navigate to Settings → Battery Health → Optimized Battery Charging.