The stock 3,000 mAh battery is completely inadequate for such a high-powered device that's has increased drain due to the higher resolution 2560x1440. The battery is not adequate even when new and once it ages, it will lose even more capacity.
they sell it so they can claim the device is the thickness of 3 credit cards while it's not all that useful. The first thing I do when I get a device is throw out the stock battery and install an aftermarket extended battery such as ZeroLemon. They make a 9,000 mAh cell that's just adequate though not excellent, you get maybe a full day with it if it's new.
tiny 3000 mAh batteries are so 2006 and just another attempt to screw the customer instead of making nice expensive long-lasting cells. But the bean counters save a little money. Extended is expensive. Instead they pour tons of money into ads convincing customers what they want is a phone with the thickness of a credit card. Not me, give me some depth to hold on to.
With these phones that are really mini-laptops with full capabilities you really need at least 9000-10,000 to make it through the day. I hate it when my phone is at 40% by noon (and declining fast) with the stock battery. The stock battery does not make it through one day, you need to find a charging outlet in the early afternoon. which will wear out your charging port eventually, as in your case.